PURIFICATION OF SPECIFIC ANTIBODIES AGAINST SARS-COV-2 PROTEIN NP USING THE FasTAG® SYSTEM

HARGUINDEGUY INES; HIRIART YANINA; CAVALITTO, SEBASTIÁN F; CAVELLO IVANA; ORTIZ, GASTÓN E

Congreso; Congreso Conjunto SAIB-SAMIGE 2021; 2021

The SARS-CoV-2 coronavirus, which causes respiratory syndrome COVID-19, has a protein nucleocapsid that envelops the viral ssRNA. The main protein of the nucleocapsid is the Np protein, which presents limited homology with nucleoproteins of other coronaviruses and therefore turns out to be an attractive antigen for the development of specific anti-Np antibodies. These antibodies can be used for the development of diagnostic systems that allow the detection of the viral antigen in infected individuals from saliva samples. In this context, our group has developed a labelling system called FasTAG®, which allows the immobilization of recombinant proteins on the surface of Gram+ formaldehyde inactivated bacteria. In this system, the recombinant proteins expressed in heterologous systems are fused to the C-terminal domain of S-Layer proteins of Lactobacillus sp. Then, the intrinsic affinity this domain possesses for the membranes of Gram+ bacteria is used for the immobilization of the recombinant proteins of interest. In this way, it is possible to purify specific antibodies against an antigen of interest. Based on the above, the objective of this work was to evaluate the functionality of the FasTAG® system to purify specific anti-Np antibodies. For this, the recombinant protein Np-FasTAG® was incubated for 12 hours at 4 ºC with a matrix made up of B. subtilis inactivated with 3% formaldehyde. Next, for the optimization of the protein fixation process to the matrix, a compound factorial design was carried out, the variables of which were: formaldehyde concentration (0.5-1.5-2.5% v/v) and time of incubation (15-30-45 minutes). The optimal condition was determined as the one that minimizes the detachment of the Np protein and maximizes the detachment of the specific antibodies. Turning out to be the optimal condition for the elaboration of the affinity matrix 2.5% v/v of formaldehyde and 15 minutes. Then, in order to evaluate the application of the affinity matrix in the purification of specific antibodies, it was incubated for 1 hour with polyclonal antibodies obtained from chicken egg yolks and the serum of goats immunized with the Np antigen. Next, to study the elution conditions of the antibodies, a compound factorial design was performed using variables: pH, time, and SDS concentration. The best elution condition was obtained for pH 10.5 and 15 minutes. Subsequently, the purified antibodies were evaluated by SDS-PAGE and ELISA. As a result, it was possible to purify 3.5 µg of anti-Np IgG and 3.1 µg of anti-Np IgY per mg of resin. Finally, the set of experiments carried out here demonstrate the potential and functionality of this system for the purification of specific anti-Np antibodies and their use for diagnostic purposes.