The SARS-CoV-2 coronavirus outbreak continues to spread at a rapid rate worldwide. The
main protease (Mpro) is an attractive target for anti-COVID-19 agents. Unexpected
difficulties have been encountered in the design of specific inhibitors. Here, by
analyzing an ensemble of ∼30 000 SARS-CoV-2 Mpro conformations from
crystallographic studies and molecular simulations, we show that small structural
variations in the binding site dramatically impact ligand binding properties. Hence,
traditional druggability indices fail to adequately discriminate between highly and
poorly druggable conformations of the binding site. By performing ∼200 virtual
screenings of compound libraries on selected protein structures, we redefine the
protein’s druggability as the consensus chemical space arising from the multiple
conformations of the binding site formed upon ligand binding. This procedure revealed a
unique SARS-CoV-2 Mpro blueprint that led to a definition of a specific structure-based
pharmacophore. The latter explains the poor transferability of potent SARS-CoV Mpro
inhibitors to SARS-CoV-2 Mpro, despite the identical sequences of the active sites.
Importantly, application of the pharmacophore predicted novel high affinity inhibitors
of SARS-CoV-2 Mpro, that were validated by
in vitro
assays performed
here and by a newly solved X-ray crystal structure. These results provide a strong basis
for effective rational drug design campaigns against SARS-CoV-2 Mpro and a new
computational approach to screen protein targets with malleable binding sites.