Fig. 2: Molecular recognition of TMPRSS2 substrates is mediated through surface loops and potentially through an unpaired cysteine residue.
From: Structure and activity of human TMPRSS2 protease implicated in SARS-CoV-2 activation
a, The substrate binding face of TMPRSS2 makes use of three disulfides (yellow sticks) and eight loops, Loops 1–3 (L1–L3) and LA–LE, to confer protein substrate specificity. Nafamostat (gray sticks) covalently bound to the catalytic Ser441 engages the S1 subsite of TMPRSS2 with residues from L1 and L2. b, Multiple sequence alignment of the TTSP family with protease subsites S1’–S4 residues highlighted. The catalytic serine residue acylated by nafamostat is denoted with an asterisk. The S2–S4 protease subsites show greater variability than S1’ and S1 and confer divergent substrate specificity within the TTSP family. c, The subsites of TMPRSS2 (blue) superposed on the corresponding residues of hepsin (magenta, PDB 1Z8G) and TMPRSS13 (orange, PDB 6KD5) with their respective KQLR and decanoyl-RVKR covalent peptide ligands. d,e, A multiple sequence alignment of the human TTSP family members (d) shows complete conservation of the interdomain Cys244-Cys365 disulfide bond but identifies TMPRSS2 as uniquely possessing the only unpaired cysteine residue, Cys379, in the SP domain (e), which is conserved among mammalian TMPRSS2 orthologs. f, The highly conserved SRCR–SP interdomain disulfide is at the backside of the SP domain and is in close proximity to the unpaired Cys379 of TMPRSS2. g, MOE protein patch analysis of the TMPRSS2 ectodomain surface reveals a contiguous 360 Å2 hydrophobic residue patch (green) highlighted with white arrows that is adjacent to the unpaired Cys379 at the backside of the SP domain.
