Probing the Dynamic Structure-Function and Structure-Free Energy Relationships of the Coronavirus Main Protease with...

The SARS-CoV-2 main protease (M^pro) is of major interest as an antiviral drug target. Structure-based virtual screening efforts, fueled by a growing list of apo and inhibitor-bound SARS-CoV/CoV-2 M^pro crystal structures, are underway in many laboratories. However, little is known about the dynamic enzyme mechanism, which is needed to inform both assay development and structure-based inhibitor design. Here, we apply biodynamics theory to characterize the structural dynamics of substrate-induced M^pro activation under nonequilibrium conditions. The catalytic cycle is governed by concerted dynamic structural rearrangements of domain 3 and the m-shaped loop (residues 132-147) on which Cys145 (comprising the thiolate nucleophile and half of the oxyanion hole) and Gly143 (comprising the second half of the oxyanion hole) reside. In particular, we observed the following: (1) Domain 3 undergoes dynamic rigid-body rotation about the domain 2-3 linker, alternately visiting two primary conformational states (denoted as M₁ ^pro ↔ M₂ ^pro); (2) The Gly143-containing crest of the m-shaped loop undergoes up and down translations caused by conformational changes within the rising stem of the loop (Lys137-Asn142) in response to domain 3 rotation and dimerization (denoted as M_1/down ^pro ↔ 2·M_2/up ^pro) (noting that the Cys145-containing crest is fixed in the up position). We propose that substrates associate to the M_1/down ^pro state, which promotes the M_2/down ^pro state, dimerization (denoted as 2·M_2/up ^pro-substrate), and catalysis. Here, we explore the state transitions of M^pro under nonequilibrium conditions, the mechanisms by which they are powered, and the implications thereof for efficacious inhibition under in vivo conditions.