Structural plasticity of SARS-CoV-2 3CL Mpro active site cavity revealed by room temperature X-ray crystallography

The COVID-19 disease caused by the SARS-CoV-2 coronavirus has become a pandemic health crisis. An attractive target for antiviral inhibitors is the main protease 3CL M pro due to its essential role in processing the polyproteins translated from viral RNA. Here we report the room temperature X-ray structure of unliganded SARS-CoV-2 3CL M pro , revealing the ligand-free structure of the active site and the conformation of the catalytic site cavity at near-physiological temperature. Comparison with previously reported low-temperature ligand-free and inhibitor-bound structures suggest that the room temperature structure may provide more relevant information at physiological temperatures for aiding in molecular docking studies. The SARS-CoV-2 3CL main protease (3CL M pro ) is a chymotrypsin-like protease that facilitates the production of non-structural proteins, which are essential for viral replication and is therefore of great interest as a drug target. Here, the authors present the 2.30 Å room temperature crystal structure of ligand-free 3CL M pro and compare it with the earlier determined low-temperature ligand-free and inhibitor-bound crystal structures.