No abstract

Transmembrane protease, serine 2 (TMPRSS2) has been identified as key host cell factor for viral entry and pathogenesis of SARS-coronavirus-2 (SARS-CoV-2). Specifically, TMPRSS2 proteolytically processes the SARS-CoV-2 Spike (S) Protein, enabling virus-host membrane fusion and infection of the lungs. We present here an efficient recombinant production strategy for enzymatically active TMPRSS2 ectodomain enabling enzymatic characterization, and the 1.95 A X-ray crystal structure. To stabilize the enzyme for co-crystallization, we pre-treated TMPRSS2 with the synthetic protease inhibitor nafamosat to form a stable but slowly reversible (15 hour half-life) phenylguanidino acyl-enzyme complex. Our study provides a structural basis for the potent but non-specific inhibition by nafamostat and identifies distinguishing features of the TMPRSS2 substrate binding pocket that will guide future generations of inhibitors to improve selectivity. TMPRSS2 cleaved recombinant SARS-CoV-2 S protein ectodomain at the canonical S1/S2 cleavage site and at least two additional minor sites previously uncharacterized. We established enzymatic activity and inhibition assays that enabled ranking of clinical protease inhibitors with half-maximal inhibitory concentrations ranging from 1.7 nM to 120 uM and determination of inhibitor mechanisms of action. These results provide a body of data and reagents to support future drug development efforts to selectively inhibit TMPRSS2 and other type 2 transmembrane serine proteases involved in viral glycoprotein processing, in order to combat current and future viral threats.