Designing of peptide aptamer targeting the receptor-binding domain of spike protein of SARS-CoV-2: an in silico study.

Short synthetic peptide molecules which bind to a specific target protein with a high affinity to exert its function are known as peptide aptamers. The high specificity of aptamers with small-molecule targets (metal ions, dyes and theophylline; ATP) is within 1 pM and 1 μM range, whereas with the proteins (thrombin, CD4 and antibodies) it is in the nanomolar range (which is equivalent to monoclonal antibodies). The recently identified coronavirus (SARS-CoV-2) genome encodes for various proteins, such as envelope, membrane, nucleocapsid, and spike protein. Among these, the protein necessary for the virus to enter inside the host cell is spike protein. The work focuses on designing peptide aptamer targeting the spike receptor-binding domain of SARS-CoV-2. The peptide aptamer has been designed by using bacterial Thioredoxin A as the scaffold protein and an 18-residue-long peptide. The tertiary structure of the peptide aptamer is modeled and docked to spike receptor-binding domain of SARS CoV2. Molecular dynamic simulation has been done to check the stability of the aptamer and receptor-binding domain complex. It was observed that the aptamer binds to spike receptor-binding domain of SARS-CoV-2 in a similar pattern as that of ACE2. The aptamer-receptor-binding domain complex was found to be stable in a 100 ns molecular dynamic simulation. The aptamer is also predicted to be non-antigenic, non-allergenic, non-hemolytic, non-inflammatory, water-soluble with high affinity toward ACE2 than serum albumin. Thus, peptide aptamer can be a novel approach for the therapeutic treatment for SARS-CoV-2.