Multifunctional protein molecular switch for antibody detection

文档序号：744314 发布日期：2021-04-23 浏览：37次中文

阅读说明：本技术 用于抗体检测的多功能蛋白分子开关 (Multifunctional protein molecular switch for antibody detection ) 是由胡接力黄爱龙李�杰于 2021-01-05 设计创作，主要内容包括：本发明公开了一种用于抗体检测的多功能蛋白分子开关,属于蛋白检测领域,所述分子开关为融合蛋白,从N端到C端,包括依次连接的如下部分：(1)SmBiT；(2)抗原表位多肽,可被待检测抗体特异性结合；(3)LgBiT。本发明的分子开关可通过抗原表位多肽与抗体特异性识别,影响SmBiT和LgBiT的结合,极大改变荧光素酶活性,导致前后荧光素酶活性变化,该变化可反映抗体浓度的高低。将本发明的分子开关用于检测新冠病毒,准确性和特异性均接近100％,具有十分良好的应用价值。(The invention discloses a multifunctional protein molecular switch for antibody detection, which belongs to the field of protein detection, and the molecular switch is fusion protein and comprises the following parts which are sequentially connected from an N end to a C end: (1) SmBiT; (2) epitope polypeptide, can be detected the antibody specificity binding; (3) LgBiT. The molecular switch disclosed by the invention can be specifically identified by the epitope polypeptide and the antibody, so that the combination of SmBiT and LgBiT is influenced, the luciferase activity is greatly changed, the change of the luciferase activity before and after the change is caused, and the change can reflect the concentration of the antibody. The molecular switch provided by the invention is used for detecting the new coronavirus, the accuracy and the specificity are close to 100%, and the molecular switch has a very good application value.)

1. A multifunctional protein molecular switch for antibody detection, characterized in that: the molecular switch is a fusion protein and comprises the following parts which are sequentially connected from an N end to a C end:

(1)SmBiT；

(2) epitope polypeptide of the antibody to be detected;

(3)LgBiT。

2. the molecular switch of claim 1, wherein: the N-terminal side of the part (1) and/or the C-terminal side of the part (3) is/are also provided with a section of epitope polypeptide which can be specifically bound by the antibody to be detected.

3. The molecular switch of claim 1 or 2, wherein: the parts (1) and (2) comprise a connecting sequence.

4. The molecular switch of claim 3, wherein: the connecting sequence is a flexible joint for expressing the fusion protein, and preferably, the connecting sequence is GS linker.

5. The molecular switch of claim 1 or 2, wherein: the epitope polypeptide is a Flag tag;

preferably, a connecting sequence is included between the parts (1) and (2);

further preferably, the linker sequence is a flexible linker for expression of the fusion protein; still further preferably, the linking sequence is a GS linker.

6. The molecular switch of claim 1 or 2, wherein: the epitope polypeptide is pG4 polypeptide;

preferably, a connecting sequence is included between the parts (1) and (2);

further preferably, the linker sequence is a flexible linker for expression of the fusion protein; still further preferably, the linking sequence is a GS linker.

7. The molecular switch of claim 1 or 2, wherein: the epitope polypeptide is a p21 polypeptide;

preferably, a connecting sequence is included between the parts (1) and (2);

further preferably, the linker sequence is a flexible linker for expression of the fusion protein; still further preferably, the linking sequence is a GS linker.

8. Use of the molecular switch of any one of claims 1 to 7 for the detection of antibodies.

9. A kit for detecting a novel coronavirus, comprising: comprising the molecular switch of claim 6 or 7.

10. The kit of claim 9, wherein: the kit also comprises a reagent for detecting the Nanoluc luciferase activity.

Technical Field

The invention belongs to the field of protein detection.

Background

The protein molecule switch is a biosensor for detecting various target biological molecules, and the principle is that the specially designed protein molecules are utilized to 'sense' and reflect the existence of the target molecules before and after being combined with the target molecules, so as to achieve the detection purpose. The protein molecular switch has wide application in disease diagnosis and biomedical basic research. Recent progress in the design of protein molecule switches is represented by the work of David Baker awarded the scientific breakthrough in 2020. They designed and constructed an artificially synthesized protein molecule switch LOCKR (Nature, 2019), and then used this system for bio-signal regulation (Nature, 2019) and more recently for detection of new coronavirus antibodies and antigens (BioRxiv, 2020).

Allosteric modulators are often used as the basis for the design of molecular switches for the detection of various protein molecules, including antibodies against viruses, and the like. Allosteric modulator enzymes, as used herein, refers to those enzymes whose enzymatic activity is altered by some conformational change. When the target molecule is not bound to the enzyme molecule, the enzyme molecule is in a state of lower (or higher) activity, and when the target molecule is bound to the enzyme molecule, the spatial structure of the enzyme molecule is changed, so that the enzyme activity is changed (higher or lower). In this case, the change in the enzymatic activity reflects the presence and amount of the target molecule. The advantage of using allosteric regulatory enzyme to detect target molecules is that the combination of target molecules and signal output occur on the same molecule, and the close coupling of the two helps to ensure the high specificity of detection, thus removing many steps such as repeated washing and buffer solution replacement, and greatly simplifying the detection process. Using similar principles, fluorescent proteins are also commonly used in molecular switch design, except that the output signal is fluorescent rather than enzymatic.

The concept of protein molecular switches has been long-standing, but the better application aspect is mainly to detect small molecules, such as calcium ions by using molecular switches constructed by fluorescent protein, calmodulin (CaM) and calmodulin-binding peptide (CaM-BP). Through the iteration improvement of recent 20 years, the molecular switch can achieve a good detection effect at present. In another example, a molecular switch constructed using Beta Lactamase (BLA) and Maltose Binding Protein (MBP) can be used to efficiently detect maltose. However, the detection of biomacromolecules with protein molecule switches is less than optimal compared to these small molecules. Taking the more studied beta galactosidase molecular switch as an example, polypeptides derived from hand-foot-and-mouth disease virus (FMDV) or HIV are respectively recombined and inserted into a specific position of the beta galactosidase to construct the molecular switch, and even if the molecular switches are fully optimized, the signal difference between the serum of a patient and the serum of a control is not more than 5 times in the best case when the molecular switches are used for detecting a serum sample. The David Baker and the like design and construct artificial molecular switches by utilizing synthetic biological means, and provide a new idea on the design basis and the path of the molecular switches, and although the molecular switches (LOCKR) designed and optimized according to the design are excellent in performance (the signal-to-noise ratio is 14 times) when detecting the S protein of the new coronavirus, the signal-to-noise ratio is only 2 times when detecting the antibody of the new coronavirus (purified polyclonal antibody). The signal to noise ratio is up to about 4-fold when detecting antibodies to hepatitis B virus (no serum test). If these molecular switches are used for real clinical sample detection, the detection signal-to-noise ratio (ratio of positive sample to negative sample) will be lower, because the clinical sample is more complex in composition and has more variable factors and interference factors. In summary, the small signal-to-noise ratio makes the existing molecular switch difficult to be truly used for clinical detection.

The Nanoluc luciferase is luciferase separated from a deep-sea shrimp animal, and has the strongest luminescence activity (the measured value of a 96-well plate can reach 10) after being modified and optimized⁸) Meanwhile, the luminous duration is long, the molecular weight is small, and the characteristics are very beneficial to the application of the compound in biomedicine. Furthermore, Dixon et al, 2015, found that a Nanoluc fragment 11 Amino Acids (AA) in length at the carboxy terminus could be separated from a large fragment at the amino terminus (under the trade name LgBiT). They further engineered and evolved the 11AA fragment to yield two new polypeptides, under the trade names SmBiT and hibit (promega), respectively. HiBiT has a high affinity for LgBiT (Kd ═ 0.7nM) and SmBiT has a low affinity for LgBiT (Kd ═ 190. mu.M), and when either HiBiT or SmBiT is separated from LgBiT, none of the fractions is enzymatically activeAnd when HiBiT or SmBiT is close to LgBiT, the Nanoluc activity is recovered.

Triana et al to investigate whether 2 target proteins interact with each other, fused 2 target proteins to SmBiT and LgBiT, respectively, showed that the 2 target proteins had an interaction relationship when luciferase activity was activated. Boursier et al express HiBiT fused to a G protein-coupled receptor (GPCR) in the cell membrane, whereby membrane surface receptor density can be detected; they also used both GPCR ligands and fluorescent markers to compete for binding to the HiBiT-GPCR fusion protein to assess ligand concentration.

At present, no report on the use of different fragments of Nanoluc luciferase for detecting antibodies is available.

Disclosure of Invention

The invention aims to solve the problems that: provides a novel multifunctional protein molecular switch for detecting antibodies.

The technical scheme of the invention is as follows:

a multifunctional protein molecular switch for antibody detection, which is a fusion protein and comprises the following parts connected in sequence from an N end to a C end:

(1)SmBiT；

(2) epitope polypeptide of the antibody to be detected;

(3)LgBiT。

further, the part (1) has an epitope polypeptide on the N-terminal side and/or the part (3) has an epitope polypeptide that can be specifically bound by the antibody to be detected.

Further, a connecting sequence is included between the parts (1) and (2).

Further, the connecting sequence is a flexible linker for expressing the fusion protein, and preferably, the connecting sequence is a GS linker.

Further, the epitope polypeptide is a Flag tag;

preferably, a connecting sequence is included between the parts (1) and (2);

further preferably, the linker sequence is a flexible linker for expression of the fusion protein; still further preferably, the linking sequence is a GS linker.

Further, the epitope polypeptide is a pG4 polypeptide;

preferably, a connecting sequence is included between the parts (1) and (2);

further preferably, the linker sequence is a flexible linker for expression of the fusion protein; still further preferably, the linking sequence is a GS linker.

Further, the epitope polypeptide is a p21 polypeptide;

preferably, a connecting sequence is included between the parts (1) and (2);

further preferably, the linker sequence is a flexible linker for expression of the fusion protein; still further preferably, the linking sequence is a GS linker.

Use of the aforementioned molecular switch for the detection of antibodies.

A kit for detecting a novel coronavirus, comprising the molecular switch as described above.

Further, the kit also comprises a reagent for detecting the Nanoluc luciferase activity.

The principle of the basic design of the present invention is shown in fig. 1. LgBiT and SmBiT are connected through epitope polypeptide of an antibody to be detected, and SmBiT can enter a specific position of the LgBiT to generate luciferase activity; when the target antibody binds to a linear epitope, steric hindrance and allosteric effects are caused, the binding strength of SmBiT and LgBiT is influenced (enhanced or weakened), and the activity of the luciferase is changed. The content of the target antibody can be reflected by the change of the fluorescence intensity by adding the luciferase substrate.

The preferred design of the invention is to add the epitope polypeptide of the antibody to be detected on the N-terminal side of SmBiT and/or the C-terminal side of LgBiT on the basis of figure 1, and the design can improve the signal-to-noise ratio of detection.

The invention has the beneficial effects that:

1. the signal to noise ratio is high. The signal-to-noise ratio of the molecular switch detection flag antibody can reach more than 30 times, and the signal-to-noise ratio of the molecular switch detection flag antibody can reach more than 200 times when a new coronavirus antibody is detected.

2. The specificity is good. Under the interference of irrelevant antibodies, the detection signals of the molecular switch of the invention can not be influenced, and the specificity for detecting the new coronavirus antibody reaches 97.0%.

3. The linear interval is wide. When detecting the new coronavirus antibody, the serum shows good linearity within 512-fold dilution, which is beneficial to quantitative analysis.

4. The accuracy is high. When detecting the new coronavirus antibody, the accuracy is as high as 97.3%.

Obviously, many modifications, substitutions, and variations are possible in light of the above teachings of the invention, without departing from the basic technical spirit of the invention, as defined by the following claims.

The present invention will be described in further detail with reference to the following examples. This should not be understood as limiting the scope of the above-described subject matter of the present invention to the following examples. All the technologies realized based on the above contents of the present invention belong to the scope of the present invention.

Drawings

FIG. 1: NanoSwitch molecular switch principle for antibody detection.

FIG. 2: NanoSwitch design and test for Flag antibody detection. A, a structure and a working schematic diagram; b, the activity change multiple of the luciferase; and C, identifying a picture by Western blot.

FIG. 3: NanoSwitch-1 × flag-2 NM. A, specificity test results with GAPDH antibody; b, 3xflag polypeptide competitive interference test results.

FIG. 4: NanoSwitch screen for detection of neo-corona antibodies.

FIG. 5: the results of the polypeptide competitive inhibition assay of NanoSwitch-PG 4/P21.

FIG. 6: dynamic detection Range of NanoSwitch-pG 4.

FIG. 7: NanoSwitch-pG4 was used to detect new coronavirus antibodies.

FIG. 8: NanoSwitch-pG4 correctly reflected the trend of new crown antibodies in new crown infected patients.

Detailed Description

The reagents and material sources used in the examples are shown in Table 1.

TABLE 1 sources of reagents and materials

The solution formulation method used in the examples:

LB liquid medium: 2g of tryptone, 1g of yeast extract and 2g of NaCl are dissolved in ddH2O, the volume is adjusted to 200ml, and the mixture is sterilized at high temperature and high pressure for 20 min.

LB solid medium: 2g of tryptone, 1g of yeast extract, 2g of NaCl and 3g of agar are dissolved in ddH2O, the volume is adjusted to 200ml, and the mixture is sterilized at high temperature and high pressure for 20 min.

Kanamycin sulfate solution (50 mg/ml): 0.5g kanamycin sulfate solid dissolved in 10ml ddH2O, 0.45um filter membrane filtration sterilization.

PBS (PH 7.4): dissolving 8g of NaCl, 0.2g of KCl, 41.78g of Na2HPO41 and 40.24g of kH2PO40 in ddH2O, adding concentrated hydrochloric acid to adjust the pH to 7.4, fixing the volume to 1L, and sterilizing at high temperature and high pressure.

20mM phosphate (PH 7.5): Na2HPO42.39g and NaH2PO40.38g, which are dissolved in 1L ddH 2O.

Binding Buffer (PH 7.5): 20mM phosphate 1L was added with 29.25g NaCl at a final concentration of 0.5M, and autoclaved.

Wash Buffer (PH 7.5): adding 1.02g of imidazole into 400mL of Binding Buffer, adjusting the pH value to 7.5 by adding sodium hydroxide, fixing the volume to 500mL, and sterilizing at high temperature and high pressure.

Output Buffer (PH 7.5): adding 5.1g of imidazole into 200mL Binding Buffer, adjusting the pH value to 7.5 by adding sodium hydroxide, fixing the volume to 300mL, and sterilizing at high temperature and high pressure.

The primer sequences used in the examples are shown in Table 2.

TABLE 2 primer sequences used in the examples of the present invention

Example 1 NanoSwitch molecular switch for Flag antibody detection

Principle one

The present example shows the basic design of the present invention by taking Flag antibody as an example. The design idea and the working principle are as follows:

(1) fusing SmBiT to the N end of LgBiT; (2) a polypeptide capable of binding to an antibody, such as 3 × flag, is inserted between LgBiT and SmBiT (fig. 2A); (3) in the absence of antibody, the SmBiT will bind to the corresponding position of LgBiT with NanoSwitch in the fully active state; (4) when specific antibodies are present and bind to specific polypeptides in NanoSwitch, steric hindrance and allosteric effects are induced, resulting in a barrier to the binding of SmBiT to LgBiT, at which time NanoSwitch will be in a partially inactivated state, showing a decrease in optical signal upon addition of substrate (fig. 2A), and thus this change in signal can be used to reflect the amount of specific antibody molecules.

Flag, also called "Flag tag", is a common artificial tag polypeptide for detecting over-expressed protein, and its sequence is: DYKDDDDK (SEQ ID NO. 20); the common alternative 3XFlag is to ligate two Flag tags, DYKDDDDK DYKDDDDK DYKDDDDK (SEQ ID NO.21), on the basis of it.

Second, method

Construction of SmBiT-LgBiT plasmid

The construction of the plasmid SmBiT-LgBiT is carried out in two steps, firstly, a transition plasmid SmBiT-HBC is constructed, and the construction process is as follows: plasmid RlucN-HBC (same as plasmid RlucN-HBC in Chinese patent application CN 201610564291.6) is used as a template, primer F G4SGG7+ R bsmb1vect is used for amplification, and the PCR reaction system is as follows: plasmid RlucN-HBC 10ng, primer F G4SGG7 (10. mu.M) and R amp (10. mu.M) were each 0.4. mu.l, 2 XPrimeSTAR Max Premix 10. mu.l, and a volume of sterilized ultrapure water was made up to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 1min, 35 cycles. The amplified fragment was recovered by using a gel recovery kit, and the recovered fragment was designated as flag 1.

The oligonucleotides F C11 oligo and R C11 oligo were annealed and 5' phosphorylated as follows: f C11 oligo 1. mu.l (100. mu.M), R C11 oligo 1. mu.l (100. mu.M), 10X T4 ligase buffer 1. mu.l, T4 polynucleotide kinase 0.5. mu.l, ddH2O 6.5.5. mu.l, total volume 10. mu.l. And (3) carrying out reaction on the reaction tube on a PCR instrument under the conditions of 37 ℃ for 30min and 95 ℃ for 5min, then entering cooling circulation, reducing the temperature by 1 ℃ in each circulation, wherein the circulation time is 15s, reducing the temperature to 25 ℃ through 70 circulation, and finishing the reaction. Taking 1 μ l of reaction product, diluting with 199 μ l of ddH2O 199, taking the diluted product (named as frag2) and performing Golden gate ligation reaction with frag1, wherein the reaction system is as follows: BsmB I enzyme 0.75. mu.l, Tango buffer 1. mu.l, DTT 1. mu.l, T7 DNA ligase 0.25. mu.l, ATP 1. mu.l, frag 31. mu.l (100ng), frag 41. mu.l, ddH2O to 10. mu.l. Reaction conditions are as follows: circulating for 20 times at 37 deg.C for 4min and 20 deg.C for 4 min. The inactivation reaction is carried out at 80 ℃ for 20 min. The product of Golden gate is transformed into JM109 competent bacteria, plates are coated, clone is initially screened, sequencing is carried out for identification, and the correct clone is named as a plasmid SmBiT-HBC.

Next, using plasmid pNanoluc (synthesized and cloned by Biotech Co., Ltd., Beijing Onck., Nanoluc luciferase gene sequence: Dixson et al, Nanoluc Complementation Reporter Optimized for Accurate Measurement of Protein Interactionsin cells ACS Chemical Biology, 2015) as a template, the PCR reaction system was: plasmid Nanoluc 10ng, primers F N11S-4 (10. mu.M) and RN11S (10. mu.M) each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and sterilized ultrapure water to make up the volume to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 20s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 3. The plasmid SmBiT-HBC is used as a template, a primer F SV40GG2+ R amp is used for amplification, and the PCR reaction system is as follows: plasmid SmBiT-HBC 10ng, primers F SV40GG2 (10. mu.M) and R amp (10. mu.M) were each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and a volume of 20. mu.l was made up with sterile ultrapure water. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 1min, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 4. The plasmid SmBiT-HBC is used as a template, a primer F amp + R G4SGG is used for amplification, and the PCR reaction system is as follows: plasmid SmBiT-HBC 10ng, primers F amp (10. mu.M) and R G4SGG (10. mu.M) were each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and a volume of 20. mu.l was made up with sterile ultrapure water. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 1min, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 5.

Carrying out Golden gate ligation reaction on the three fragments obtained above, namely frag3, frag4 and frag5, wherein the reaction system is as follows: BsmB I enzyme 0.75. mu.l, Tango buffer 1. mu.l, DTT 1. mu.l, T7 DNA ligase 0.25. mu.l, ATP 1. mu.l, frag 31. mu.l (15ng), frag 42. mu.l (60ng), frag 51. mu.l (60ng) ddH2O to 10. mu.l. Reaction conditions are as follows: circulating for 20 times at 37 deg.C for 4min and 20 deg.C for 4 min. The inactivation reaction is carried out at 80 ℃ for 20 min. The product of Golden gate is transformed into JM109 competent bacteria, plates are coated, clone is initially screened, sequencing is carried out for identification, and the correct clone is named as a plasmid SmBiT-LgBiT.

2. Construction of plasmid NanoSwitch-3 × flag

The plasmid SmBiT-LgBiT is taken as a template, and the primer F3 flag GS + R amp is used for amplification. The PCR reaction system is as follows: plasmid SmBiT-LgBiT 10ng, primers F3 flag GS (10. mu.M) and R amp (10. mu.M) each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, sterile ultrapure water to make up the volume to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 30s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 6.

The plasmid SmBiT-LgBiT is taken as a template, and the amplification is carried out by using a primer R3 flag GS + F amp. The PCR reaction system is as follows: plasmid SmBiT-LgBiT 10ng, primers R3 flag GS (10. mu.M) and F amp (10. mu.M) each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and sterilized ultrapure water to make up the volume to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 30s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 7.

The oligonucleotides F3 flag oligo and R3 flag oligo were annealed and 5' phosphorylated, the reaction system was as follows: mu.l of F3 flag oligo (100. mu.M), 1. mu.l of R3 flag oligo (100. mu.M), 1. mu.l of 10X T4 ligase buffer, 0.5. mu.l of T4 polynucleotide kinase, and 6.5. mu.l of ddH2O 6.5 in a total volume of 10. mu.l. And (3) carrying out reaction on the reaction tube on a PCR instrument under the conditions of 37 ℃ for 30min and 95 ℃ for 5min, then entering cooling circulation, reducing the temperature by 1 ℃ in each circulation, wherein the circulation time is 15s, reducing the temperature to 25 ℃ through 70 circulation, and finishing the reaction. Mu.l of the reaction product was taken and diluted with 199. mu.l of ddH2O 199, and the fragment was named frag 8.

Carrying out Golden gate ligation reaction on the three fragments obtained above, namely frag6, frag7 and frag8, wherein the reaction system is as follows: BsmB I enzyme 0.75. mu.l, Tango buffer 1. mu.l, DTT 1. mu.l, T7 DNA ligase 0.25. mu.l, ATP 1. mu.l, frag 61. mu.l (50ng), frag 71. mu.l (50ng), frag 81. mu.l ddH2O were supplemented to 10. mu.l. Reaction conditions are as follows: circulating for 20 times at 37 deg.C for 4min and 20 deg.C for 4 min. The inactivation reaction is carried out at 80 ℃ for 20 min. The product of Golden gate is transformed into JM109 competent bacteria, plated, initially screened for clone, sequenced and identified, and the correct clone is named as the plasmid NanoSwitch-3 × flag.

The molecular switch gene sequence of NanoSwitch-3 × flag (SEQ ID NO.22) is as follows:

note: the initial 3 bases and the terminal 3 bases of the sequence are respectively an initiation codon and a termination codon, the single underlined and non-bold part is SmBiT, the lower case part is a connecting sequence GS linker, the double underlined part is3 × flag, and the single underlined and bold part is LgBiT. GS linker is a polypeptide consisting of amino acids G and S, and has a plurality of permutation and combination forms, and can be used for replacing the connection sequence of a molecular switch of NanoSwitch-3 × flag conventionally.

Flag antibody assay

HEK293 cells were transfected with the plasmid NanoSwitch-3 × flag, and after 48 hours, the cells were lysed by repeated freeze-thawing with liquid nitrogen, and then 9 μ l of the lysate was added with 1 μ l (1 μ g) of the flag antibody (1 μ g of the GAPDH antibody was added to the control group), incubated at 37 ℃ for 1 hour, and then assayed for Nanoluc activity using a commercially available Nanoluc assay reagent (Promega).

Three, result in

The results show that the addition of the flag antibody reduced the signal by an average of 3.9-fold compared to the control group (FIG. 2B).

The results of this example show that the molecular switch of the present invention can effectively realize the detection of antibodies.

Example 2 improvement of NanoSwitch-3 × flag

The purpose of this example is to provide three improvements based on example 1.

The improvement scheme 1: 3 1 × flag are respectively placed at the N end of SmBiT, between SmBiT and LgBiT and at the C end of LgBiT (NanoSwitch-1 × flag-3);

in the improvement scheme 2, only the first two 1 × flags are reserved on the basis of the improvement scheme 1; (NanoSwitch-1 × flag-2NM), and the 1 × flag at the C terminal is removed.

In the improvement scheme 3, on the basis of the improvement scheme 1, 1 × flag at the N end is removed, and the last two 1 × flags (NanoSwitch-1 × flag-2MC) are reserved.

Method and device

1. Construction of plasmid NanoSwitch-1 × flag-2MC

The plasmid NanoSwitch-3 × flag was used as a template, and amplified with primers F flag-SV40+ R amp. The PCR reaction system is as follows: plasmid C11-3flag-N11S 10ng, primers F flag-SV40 (10. mu.M) and R amp (10. mu.M) were each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and a volume of sterilized ultrapure water was made up to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 30s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 9.

The plasmid NanoSwitch-3 × FLAG is taken as a template, and the primer R FLAG-N11S + F C11-FLAG is used for amplification. The PCR reaction system is as follows: plasmid C11-3FLAG-N11S 10ng, primers R FLAG-N11S (10. mu.M) and F C11-FLAG (10. mu.M) each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, sterile ultrapure water make-up volume to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 20s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 10.

The plasmid NanoSwitch-3 × FLAG was used as a template, and amplified with primer F amp + R C11-FLAG. The PCR reaction system is as follows: plasmid C11-3FLAG-N11S 10ng, primers F amp (10. mu.M) and R C11-FLAG (10. mu.M) each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, sterile ultrapure water make-up volume to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 30s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 11.

Carrying out Golden gate ligation reaction on the three fragments obtained above, namely frag9, frag10 and frag11, wherein the reaction system is as follows: BsmB I enzyme 0.75. mu.l, Tango buffer 1. mu.l, DTT 1. mu.l, T7 DNA ligase 0.25. mu.l, ATP 1. mu.l, frag 91. mu.l (40ng), frag 101. mu.l (10ng), frag 111. mu.l (40ng) ddH2O to 10. mu.l. Reaction conditions are as follows: circulating for 20 times at 37 deg.C for 4min and 20 deg.C for 4 min. The inactivation reaction is carried out at 80 ℃ for 20 min. The product of Golden gate is transformed into JM109 competent bacteria, plated, initially screened for clone, sequenced and identified, and the correct clone is named as the plasmid NanoSwitch-1 × flag-2 MC.

The molecular switch gene sequence (SEQ ID NO.23) of NanoSwitch-1 × flag-2MC is as follows:

note: the initial 3 and terminal 3 bases of the sequence are respectively an initiation codon and a termination codon, the single underlined and non-bold part is SmBiT, the lower case part is a connecting sequence (GS linker), the double underlined part is 1 × flag, and the single underlined and bold part is LgBiT.

2.NanoSwitch-1×flag-3

The plasmid NanoSwitch-1 × flag-2MC is used as a template, and the primer F flag-C11+ R amp is used for amplification. The PCR reaction system is as follows: plasmid C11-nogS-flag-10GS-N11S-nogS-flag10ng, primers F flag-C11 (10. mu.M) and R amp (10. mu.M) were each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and the volume of sterilized ultrapure water was made up to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 30s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 12.

The plasmid NanoSwitch-1 × flag-2MC is used as a template, and the primer R flag-C11+ Famp is used for amplification. The PCR reaction system is as follows: plasmid C11-nogS-flag-10GS-N11S-nogS-flag10ng, primers R flag-C11 (10. mu.M) and F amp (10. mu.M) were each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and the volume of sterilized ultrapure water was made up to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 30s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 13.

Performing Golden gate ligation reaction on the two fragments frag12 and frag13 obtained in the step (a) in a reaction system: BsmB I enzyme 0.75. mu.l, Tango buffer 1. mu.l, DTT 1. mu.l, T7 DNA ligase 0.25. mu.l, ATP 1. mu.l, frag 121. mu.l (50ng), frag 131. mu.l (40ng) ddH2O were supplemented to 10. mu.l. Reaction conditions are as follows: circulating for 20 times at 37 deg.C for 4min and 20 deg.C for 4 min. The inactivation reaction is carried out at 80 ℃ for 20 min. The product of Golden gate is transformed into JM109 competent bacteria, plated, initially screened for clone, sequenced and identified, and the correct clone is named as the plasmid NanoSwitch-1 × flag-3.

The molecular switch gene sequence (SEQ ID NO.24) of NanoSwitch-1 × flag-3 is as follows:

note: the initial 3 and terminal 3 bases of the sequence are respectively an initiation codon and a termination codon, the single underlined and non-bold part is SmBiT, the lower case part is a connecting sequence (GS linker), the double underlined part is3 × flag, and the single underlined and bold part is LgBiT.

3.NanoSwitch-1×flag-2NM

The plasmid NanoSwitch-1 × flag-3 was used as a template, and amplified with primer F SV40GG2+ R amp. The PCR reaction system is as follows: plasmid Flag-nogS-C11-nogS-Flag-10GS-N11S-nogS-Flag10ng, primers F SV40GG2 (10. mu.M) and R amp (10. mu.M) were each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and a sterile ultrapure water was made up to a volume of 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 30s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 14.

The plasmid NanoSwitch-1 × flag-3 was used as a template, and amplified with primer R N11S-del + Famp. The PCR reaction system is as follows: plasmid Flag-nogS-C11-nogS-Flag-10GS-N11S-nogS-Flag10ng, primer R N11S-del (10. mu.M) and F amp (10. mu.M) were each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and a sterile ultrapure water was filled up to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 30s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 15.

Performing Golden gate ligation reaction on the two fragments frag14 and frag15 obtained in the step (a) in a reaction system: BsmB I enzyme 0.75. mu.l, Tango buffer 1. mu.l, DTT 1. mu.l, T7 DNA ligase 0.25. mu.l, ATP 1. mu.l, frag 141. mu.l (50ng), frag 151. mu.l (30ng) ddH2O were supplemented to 10. mu.l. Reaction conditions are as follows: circulating for 20 times at 37 deg.C for 4min and 20 deg.C for 4 min. The inactivation reaction is carried out at 80 ℃ for 20 min. The product of Golden gate is transformed into JM109 competent bacteria, plated, initially screened for clone, sequenced and identified, and the correct clone is named as the plasmid NanoSwitch-1 × flag-2 NM.

The molecular switch gene sequence (SEQ ID NO.25) of NanoSwitch-1 × flag-2NM is as follows:

note: the initial 3 and terminal 3 bases of the sequence are respectively an initiation codon and a termination codon, the single underlined and non-bold part is SmBiT, the lower case part is a connecting sequence (GS linker), the double underlined part is3 × flag, and the single underlined and bold part is LgBiT.

Flag antibody detection

The constructed expression plasmids were transfected into HEK293 cells, 9. mu.l of the lysate was added with 1. mu.l (1. mu.g) of flag antibody (1. mu.g of GAPDH antibody was added to the control group), and the Nanoluc activity was detected after incubation at 37 ℃ for 1 hour.

5. Affinity purification validation

To further prove that the flag antibody can be bound to the NanoSwitch with the flag polypeptide, the inventor uses the flag antibody or the GAPDH antibody to respectively incubate HEK293 cell lysate expressing NanoSwitch-1 Xflag-2 NM, then uses Protein A agarose beads for affinity purification, and uses the obtained product for Western blot identification.

Second, result in

Flag antibody detection

The addition of the flag antibody reduced the NanoSwitch-1 × flag-3 signal by an average of 20.5 times, the NanoSwitch-1 × flag-2NM signal by an average of 33.1 times, and the NanoSwitch-1 × flag-2MC signal by an average of 30.9 times, as compared to the control group (FIG. 2B).

2. Affinity purification validation

The NanoSwitch-1 × flag-2NM was precipitated by the flag antibody, whereas the GAPDH antibody was not (FIG. 2C). Indicating that the flag antibody did bind to the NanoSwitch-1 × flag-2NM molecule in its native state.

The results of this example show that the three improved schemes significantly improve the detection signal-to-noise ratio compared with the basic design of example 1.

EXAMPLE 3NanoSwitch-1 × flag-2 specificity test for detecting flag antibody

The NanoSwitch-1 × flag-2NM is subjected to prokaryotic expression and purification, and the detection specificity of the flag antibody is further proved.

Method and device

1. Plasmid construction and prokaryotic expression purification

Plasmid PET28a was used as a template, and amplified with the primer F PET28a-Chis2+ R rop-bsa 1. The PCR reaction system is as follows: plasmid PET28a 10ng, primers F PET28a-Chis2 (10. mu.M) and R rop-bsa1 (10. mu.M) each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and a volume of sterilized ultrapure water was made up to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 45s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 16.

The plasmid PET28a was used as a template, and the plasmid was amplified with the primer R PET28a-Chis3+ F rop-bsal. The PCR reaction system is as follows: plasmid PET28a 10ng, primers R PET28a-Chis3 (10. mu.M) and F rop-bsal (10. mu.M) each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and a volume of sterilized ultrapure water was made up to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 45s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 17.

The plasmid NanoSwitch-1 × flag-2 is taken as a template, and the primer F pet28a-flag2+ R pet28a-flag is used for amplification. The PCR reaction system is as follows: plasmid NanoSwitch-1 × flag-210ng, primers F pet28a-flag2(10 μ M) and R pet28a-flag (10 μ M) each 0.4 μ l, 2X PrimeSTAR Max Premix 10 μ l, and a sterile ultrapure water makeup volume to 20 μ l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 20s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 18.

Carrying out Golden gate ligation reaction on the three fragments obtained above, namely frag16, frag17 and frag18, wherein the reaction system is as follows: bsa1 enzyme 0.75. mu.l, Tango buffer 1. mu.l, DTT 1. mu.l, T7 DNA ligase 0.25. mu.l, ATP 1. mu.l, frag 161. mu.l (60ng), frag 171. mu.l (60ng), frag 181. mu.l (15ng) ddH2O were supplemented to 10. mu.l. Reaction conditions are as follows: circulating for 20 times at 37 deg.C for 4min and 20 deg.C for 4 min. The inactivation reaction is carried out at 80 ℃ for 20 min. The product of Golden gate is transformed into JM109 competent bacteria, plated, initially screened for clone, sequenced and identified, and the correct clone is named as plasmid PET-NanoSwitch-1 × flag-2.

The correctly sequenced plasmid PET-NanoSwitch-1 × flag-2 was transformed into Rosetta (DE3), spread on LB plates containing 50ug/ml kanamycin sulfate and cultured at 37 ℃ for 16 h. Single colonies were removed to 5ml LB medium containing 50ug/ml kanamycin sulfate at 37 ℃ at 220rpm for 16 h. 5ml of the bacterial suspension was inoculated into 200ml of LB medium containing 50ug/ml kanamycin sulfate, and cultured at 37 ℃ and 220rpm until OD becomes 0.6 (about 3 hours). IPTG was added to a final concentration of 1mM, 16 ℃, 180rpm, 16 h. The bacterial solution was transferred to a centrifuge tube and centrifuged at 4000rpm for 15min at 4 ℃. The supernatant was discarded and resuspended in PBS at 4 ℃ and 4000rpm for 15 min. Discarding the supernatant, adding 80ml Binding Buffer for resuspension, and performing ultrasonic bacteria breaking. Collecting the broken bacteria solution at 4 deg.C and 12000rpm for 20min, and collecting the supernatant. The nickel column was washed twice with ddH2O and twice with Binding Buffer, and the supernatant from step 8 was applied to the column for 6 s/drop. Wash Buffer column 3 times, add 20ml Elution Buffer to elute target protein. The eluted protein was added to a 3KD ultrafilter tube and centrifuged at 4000rpm at 4 ℃ until 2ml of the remaining liquid remained. 8ml of PBS solution was added and centrifuged at 4000rpm at 4 ℃ until 2ml of liquid remained. Repeat 3 times. The protein in the ultrafiltration tube was aspirated, the concentration measured and stored at 4 ℃.

2. Specificity test with GAPDH antibody

The flag antibody and GAPDH antibody were diluted in duplicate and detected with NanoSwitch-1 × flag-2NM purified by prokaryotic expression.

3.3 × flag polypeptide competitive interference test

3 × flag polypeptide is synthesized, added into a NanoSwitch-1 × flag-2NM + flag antibody reaction system in different concentrations, and then the change condition of the Nanoluc activity of the NanoSwitch-1 × flag-2NM + flag antibody is detected. 100 ug/ml of unrelated polypeptide p21 or pG4 was used as a control, and added to the NanoSwitch-1 × flag-2NM + flag antibody reaction system.

Second, result in

1. Specificity test with GAPDH antibody

The results show (fig. 3A) that the Nanoluc activity gradually decreased with increasing amounts of flag antibody, while the Nanoluc activity was not significantly altered by increasing amounts of GAPDH antibody.

The results show that: the change of the signal of NanoSwitch-1 × flag-2NM has good specificity, and when the concentration of the flag antibody is 1.6-51.2 μ g/ml, the signal and the concentration of the antibody have good dose-dependent relationship.

2.3 × flag polypeptide competitive interference test

The higher the concentration of the 3 × flag polypeptide (flag pep) added, the more the Nanoluc activity of the reaction system gradually recovers due to its competitive binding with the flag antibody. Whereas unrelated polypeptides p21 or pG4 failed to alter the Nanoluc activity.

The results show that: the binding of the flag antibody to the NanoSwitch-1 × flag-2NM has specificity, and the binding causes the NanoLuc enzyme activity of the NanoSwitch-1 × flag-2NM to be decreased, so that the signal change thereof can reflect the amount of the flag antibody.

In conclusion, NanoSwitch-1 × flag-2NM can specifically detect the flag antibody.

EXAMPLE 4 NanoSwitch molecular switch for detection of New coronavirus (SARS-CoV-2)

Two polypeptides, pG4 and p21, were used and placed into the NanoSwitch in three different ways. The first is only 1 copy at the C-terminal (marked as pG4-C and p21-C), the second is only 1 copy between LgBiT and SmBiT (marked as pG4-M and p21-M), the third is 1 copy between LgBiT and SmBiT, the N-terminal is 1 copy (marked as pG4-MC and p21-MC), the fourth is a combination of the two, and contains two copies of polypeptide (marked as pG4-NM and p21-NM), and the fifth is that 1 copy is added at the N-terminal (marked as pG4-NMC and p21-NMC) on the basis of the third.

The polypeptide sequence of pG4 (SEQ ID NO.26) is as follows:

LQPELDSFKEELDKYFKNHTSPDVD

the polypeptide sequence of p21 (SEQ ID NO.27) is as follows:

PSKPSKRSFIEDLLFNKV

method and device

A plasmid expressing the aforementioned NanoSwitch was synthesized by the methods of examples 1 and 2. Compared to the plasmids obtained in examples 1 and 2, the plasmid synthesized in this example only involved the replacement of the Flag or 3xflag gene sequence with that of pG4 or p21, wherein the gene sequence of pG4 (SEQ ID No.28) is:

TTGCAACCTGAATTAGACTCATTCAAGGAGGAGTTAGATAAATATTTTAAGAATCATACATCACCAGATGTTGAT

the gene sequence of p21 (SEQ ID NO.29) is:

CCATCAAAACCAAGCAAGAGGTCATTTATTGAAGATCTACTTTTCAACAAAGTG

the plasmids were transfected into HEK293 cells, and then 9. mu.l of the lysate was diluted and added to 1. mu.l of serum from a new corona infected patient (4 patients), while the serum from a hepatitis B virus infected patient or the serum from a healthy human was used as a control. After incubation for 20min at room temperature, the Nanoluc activity in the system was directly detected.

Second, result in

The results are shown in FIG. 4.

Both polypeptides adopt the first and second configurations, i.e. a single copy does not reflect the new coronavirus antibody profile in serum.

And the third, fourth and fifth constructions can reflect the antibody condition, wherein the fourth construction detects a relatively higher signal-to-noise ratio, and the molecular switches for detecting pG4 and p21 antibodies are named NanoSwitch-pG4 and NanoSwitch-p21, respectively. Compared with the two polypeptides, pG4 was detected more effectively than p 21. For example, for sample No. 1, the signal for pG4-MC increased 223-fold over healthy control serum.

It is noted that, unlike the NanoSwitch that detects the flag antibody in examples 1 and 2, both NanoSwitch-pG4 and NanoSwitch-p21 exhibited increased, but not decreased, Nanoluc activity after the addition of serum from a new coronary patient.

The above results indicate that, in the case of the pG4 antibody or the p21 antibody, an antigenic polypeptide is required between LgBiT and SmBiT on the C-terminal side and/or N-terminal side in addition to the antigenic polypeptide. And the luciferase activity increases rather than decreases upon detection of the target antibody.

Example 5 competitive inhibition assay of NanoSwitch-pG4 and NanoSwitch-p21

To demonstrate the specificity of NanoSwitch-pG4 and NanoSwitch-p21 for detecting antibodies to the novel coronaviruses, a competitive inhibition assay was performed. The inventors synthesized two polypeptides of pG4 and p21, added the two polypeptides at different concentrations to the NanoSwitch + neo-corona serum system of the 4 th configuration of example 4, and then detected the Nanoluc activity.

The results show that the Nanoluc activity of both molecular switches gradually decreases with increasing concentration of specific polypeptide (fig. 5).

This indicates that the neo-corona antibodies in serum are able to specifically bind to both NanoSwitch molecules described above.

Example 6NanoSwitch-pG4 dynamic Range of detection of New coronavirus antibodies

1. Method of producing a composite material

Prokaryotic expression of NanoSwitch-pG4 having the fourth structure (i.e., the pG4 polypeptide at the middle and C-terminal) in example 4, gradient dilution of serum of patients with new coronavirus pneumonia with higher titer, and linear range detection.

The prokaryotic expression method comprises the following steps:

construction of plasmid PET-NanoSwitch-pG4

Plasmid PET28a was used as a template, and the amplification was carried out with the primer R PET28a-Chis2+ F rop-bsa 1. The PCR reaction system is as follows: plasmid PET28a 10ng, primers R PET28a-Chis2 (10. mu.M) and F rop-bsa1 (10. mu.M) each 0.4. mu.l, 2X PrimeSTAR Max Premix 10. mu.l, and a volume of sterilized ultrapure water was made up to 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 45s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 20.

The plasmid SmBiT-LgBiT-2xpG4-MC is used as a template and is amplified by a primer F pet28a-cov + R pet28 a-cov. The PCR reaction system is as follows: plasmid SmBiT-LgBiT-2xpG4-MC 10ng, 0.4. mu.l each of primers F pet28a-cov (10. mu.M) and R pet28a-cov (10. mu.M), 2X PrimeSTAR Max Premix 10. mu.l, and a sterile ultrapure water makeup volume of 20. mu.l. Reaction conditions are as follows: pre-denaturation at 95 ℃ for 3 min; 95 ℃ for 15s, 55 ℃ for 15s, 72 ℃ for 20s, 35 cycles. The amplified fragment was recovered with a gel recovery kit, and the recovered fragment was named frag 21.

Carrying out Golden gate ligation reaction on the three fragments obtained above, namely frag19, frag20 and frag21, wherein the reaction system is as follows: bsa1 enzyme 0.75. mu.l, Tango buffer 1. mu.l, DTT 1. mu.l, T7 DNA ligase 0.25. mu.l, ATP 1. mu.l, frag 191. mu.l (60ng), frag 201. mu.l (60ng), frag 211. mu.l (15ng) ddH2O were supplemented to 10. mu.l. Reaction conditions are as follows: circulating for 20 times at 37 deg.C for 4min and 20 deg.C for 4 min. The inactivation reaction is carried out at 80 ℃ for 20 min. The product of Golden gate was transformed into JM109 competent bacteria, plated, clone screened, sequenced and identified, and the correct clone was designated plasmid pET-NanoSwitch-pG 4.

② prokaryotic expression and purification of NanoSwitch-pG4

The correctly sequenced plasmid pET-NanoSwitch-pG4 was transformed into Rosetta (DE3), spread on LB plates containing 50ug/ml kanamycin sulfate, and cultured at 37 ℃ for 16 h. Single colonies were removed to 5ml LB medium containing 50ug/ml kanamycin sulfate at 37 ℃ at 220rpm for 16 h. 5ml of the bacterial suspension was inoculated into 200ml of LB medium containing 50ug/ml kanamycin sulfate, and cultured at 37 ℃ and 220rpm until OD becomes 0.6 (about 3 hours). IPTG was added to a final concentration of 1mM, 16 ℃, 180rpm, 16 h. The bacterial solution was transferred to a centrifuge tube and centrifuged at 4000rpm for 15min at 4 ℃. The supernatant was discarded and resuspended in PBS at 4 ℃ and 4000rpm for 15 min. Discarding the supernatant, adding 80ml Binding Buffer for resuspension, and performing ultrasonic bacteria breaking. Collecting the broken bacteria solution at 4 deg.C and 12000rpm for 20min, and collecting the supernatant. The nickel column was washed twice with ddH2O and twice with Binding Buffer, and the supernatant from step 8 was applied to the column for 6 s/drop. Wash Buffer column 3 times, add 20ml Elution Buffer to elute target protein. The eluted protein was added to a 3KD ultrafilter tube and centrifuged at 4000rpm at 4 ℃ until 2ml of the remaining liquid remained. 8ml of PBS solution was added and centrifuged at 4000rpm at 4 ℃ until 2ml of liquid remained. Repeat 3 times. The protein in the ultrafiltration tube was aspirated, the concentration measured and stored at 4 ℃.

2. Results

Prior to the sample being diluted 512-fold, the Nanoluc activity decreased with increasing dilution, showing a wider linear range (fig. 6).

Example 7NanoSwitch-pG4 for serum antibody detection in New coronavirus infected persons

1. Method of producing a composite material

198 sera from non-neocorona-infected persons and 111 sera positive for neocorona antibodies were examined with NanoSwitch-pG4 obtained from prokaryotic expression in example 6. These serum samples of the new crown-infected patients, which were derived from a previous study, were tested for positive for new crown antibodies using a kit that has been approved for clinical detection of new crown antibodies (antibodies responses to SARS-CoV-2in tissues with COVID-19.Nature Medicine, 2020).

The detection process is as follows: prokaryotic expression purified NanoSwitch-pG40.05ng (dissolved in 9. mu.l buffer (50mM Hepes (pH7.5), 3mM EDTA, 150mM NaCl, 0.005% (v/v) Tween-20, 10mM DTT) as follows) was taken, and 1. mu.l of serum was added to the system, incubated at 37 ℃ for 10min, and then directly detected with NanoLuc detection reagent (Promega).

The test result shows that the NanoSwitch-pG4 can well distinguish the positive and negative of the new crown antibody, and the AUC in ROC is 0.9909(P is less than 0.0001) (FIG. 7A). When the Cutoff value was 1265, the sensitivity and specificity reached 97.3% and 97.0%, respectively (fig. 7B).

Based on this cutoff value, the inventors calculated a new crown antibody titer value for each test sample, and plotted an antibody titer change curve based on the measured values of serum samples from the same patient. As a result, it was found that the trend of the antibody titer measured according to the method was in good agreement with the trend of the antibody titer measured by magnetic particle chemiluminescence (MCLIA, approved for clinical examination), and completely reflected the process of the antibody turning from negative to positive in the early stage of infection and the subsequent increase or decrease of the antibody (FIG. 8 shows the details of 6 patients). Compared with a magnetic particle chemiluminescence method, the method has the advantages that detection steps are greatly reduced, various steps of washing and buffer solution replacement are completely omitted, the steps of sample adding, incubation and detection are completed only, and the detection time is within 45 min. Meanwhile, the sample only needs 1 mul, and does not need to be diluted, so the method is very simple and convenient.

The results of this example show that the NanoSwitch-pG4 of the invention can be used for detecting the new coronavirus antibody, and the process is simple and has high accuracy.

In conclusion, the molecular switch for antibody detection can effectively detect various antibodies, and has the advantages of large detection linear range, high specificity and high accuracy.

SEQUENCE LISTING

<110> Chongqing university of medical science

<120> multifunctional protein molecular switch for antibody detection

<130> GY363-2020P0112063CCR4

<160> 29

<170> PatentIn version 3.5

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ttcggacggc cgtatgaagg catcgccgtg ttcgacggca aaaagatcac tgtaacaggg 480

accctgtgga acggcaacaa aattatcgac gagcgcctga tcacccccga cggctccatg 540

ctgttccgag taaccatcaa ctcagattac aaggatgacg acgataagta a 591

<210> 24

<211> 615

<212> DNA

<213> Artificial sequence

<400> 24

atggattaca aggatgacga cgataaggtg accggctacc ggctgttcga ggagattctc 60

gactacaaag atgatgacga taaaggaggt ggtggatctg gaggaggtgg atctgtcttc 120

acactcgaag atttcgttgg ggactgggaa cagacagccg cctacaacct ggaccaagtc 180

cttgaacagg gaggtgtgtc cagtttgctg cagaatctcg ccgtgtccgt aactccgatc 240

caaaggattg tccggagcgg tgaaaatgcc ctgaagatcg acatccatgt catcatcccg 300

tatgaaggtc tgagcgccga ccaaatggcc cagatcgaag aggtgtttaa ggtggtgtac 360

cctgtggatg atcatcactt taaggtgatc ctgccctatg gcacactggt aatcgacggg 420

gttacgccga acatgctgaa ctatttcgga cggccgtatg aaggcatcgc cgtgttcgac 480

ggcaaaaaga tcactgtaac agggaccctg tggaacggca acaaaattat cgacgagcgc 540

ctgatcaccc ccgacggctc catgctgttc cgagtaacca tcaactcaga ttacaaggat 600

gacgacgata agtaa 615

<210> 25

<211> 591

<212> DNA

<213> Artificial sequence

<400> 25