Conformational Perturbation of SARS-CoV-2 Spike Protein Using N-Acetyl Cysteine, a Molecular Scissor: A Probable Strategy to Combat COVID-19

The infection caused by Severe Acute Respiratory Syndrome–CoronaVirus-2 (SARS-CoV-2) resulted in a pandemic across the globe with a huge death toll. The symptoms from SARS-CoV2 appear somewhat similar to the SARS-CoV-1 infection that appeared in early 21st century but the infectivity is far higher for the SARS-CoV-2. The virus attaches itself to exposed human epithelial cells through the spike protein. Recently discovered crystal structure of the complex of spike protein of SARS-CoV-2 with human angiotensin-converting enzyme 2 (ACE2) receptor indicated that the virus binds with the host cell very strongly. We hypothesized that the perturbation of the functionally active conformation of spike protein through the reduction of a solvent accessible disulfide bond (Cys391-Cys525) that provides its structural architecture, may 2 be a feasible strategy to disintegrate the spike protein from ACE2 receptor and thereby prevent the infection. Using in silico platform we showed that N-acetyl cysteine (NAC), a drug used as antioxidant and mucolytic agent, binds in the close proximity of above disulfide bond. The reduction of the disulfide bond via thiol/disulfide exchange, followed by covalent conjugation of NAC perturbed the stereo specific orientations of interacting key residues of spike protein. This resulted in threefold weakening in the binding affinity of spike protein with ACE2 receptor. This opens avenues for exploring the effect of NAC in vitro, ex vivo and in vivo and on successful observation of the similar effect as in silico, the intervention of NAC may be translated in the pharmacoprevention and treatment of Corona virus disease 2019.