The molecular basis of TMPRSS2 and Spike interplay in SARS-CoV-2 infection

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) depends on angiotensin-converting enzyme 2 (hACE2) alone in entering the host cell. But in the presence of transmembrane protease serine 2 (TMPRSS2), SARS-CoV-2 surface protein (Spike) gets primed and changes the infection route from receptor-mediated endocytosis to membrane fusion, causing faster viral entry and strong cytopathic effects of syncytia formation. Interestingly, we found that the TMPRSS2 cytosolic tail has several tyrosine residues that can be phosphorylated by the host-cell kinases. We identified the Abelson kinase (Abl) to physically interact with TMPRSS2 and to phosphorylate up to six tyrosine residues in the TMPRSS2 cytosolic tail. Interestingly the phosphomimetic TMPRSS2 mutant is less active as serine protease. This mutant slows down SARS-CoV-2 pseudovirus infection and Spike-mediated cell-cell fusion. Furthermore, co-immunoprecipitation experiments revealed a robust TMPRSS2-Spike interaction. Mutagenesis studies pinpointed the TMPRSS2 binding region within the scavenger receptor cysteine-rich domain (SRCR). Deletion of 21 amino acids inside this region diminished TMPRSS2-supportive effects on SARS-CoV-2 pseudovirus infection. Next, we synthesized the 21 aa peptide and showed that the peptide inhibits SARS-CoV-2 pseudovirus infection even in the absence of TMPRSS2, suggesting the peptide competes with all the other serine proteases involved in SARS-CoV2 infection. Thus, the 21 aa peptide might be used as a pan-inhibitor. Our findings path the way for novel inhibitors of infection of SARS-CoV-2 and other serine protease dependent viruses.