Intracellular autoactivation of TMPRSS11A, an airway epithelial transmembrane serine protease

Abstract

Type II transmembrane serine proteases (TTSPs) are a group of enzymes participating in diverse biological processes. Some members of the TTSP family are implicated in viral infection. TMPRSS11A is a TTSP expressed on the surface of airway epithelial cells, which has been shown to cleave and activate spike proteins of the severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome coronaviruses (CoVs). In this study, we examined the mechanism underlying the activation cleavage of TMPRSS11A that converts the one-chain zymogen to a two-chain enzyme. By expression in human embryonic kidney 293, esophageal EC9706 and lung epithelial A549 and 16HBE cells, western blotting, and site-directed mutagenesis, we found that the activation cleavage of human TMPRSS11A was mediated by autocatalysis. Moreover, we found that TMPRSS11A activation cleavage occurred before the protein reached the cell surface, as indicated by studies with trypsin digestion to remove cell surface proteins, treatment with cell organelle-disturbing agents to block intracellular protein trafficking, and analysis of a soluble form of TMPRSS11A without the transmembrane domain. We also showed that TMPRSS11A was able to cleave the SARS-CoV-2 spike protein. These results reveal an intracellular autocleavage mechanism in TMPRSS11A zymogen activation, which differs from the extracellular zymogen activation reported in other TTSPs. These findings provide new insights into the diverse mechanisms in regulating TTSP activation.

Structure, activity and inhibition of human TMPRSS2, a protease implicated in SARS-CoV-2 activation

“…Our demonstration that TMPRSS2 can cleave the multibasic S1/S2 site of the S protein suggests that instead of conferring furin dependence, the virulent properties of this site may derive from promiscuous recognition and cleavage by airway-expressed TTSPs, which is supported by the demonstrated roles that TMPRSS4 35,36 , TMPRSS11d 20,37,38 , and TMPRSS13 20,37 , which colocalize with ACE2 36 , play in enabling SARS-CoV-2 infection across various tissues.…”

Priming of SARS-CoV-2 S protein by several membrane-bound serine proteinases could explain enhanced viral infectivity and systemic COVID-19 infection

“…These authors also demonstrate significant priming potential of three members of the HAT/DESC subgroup of membrane serine proteinases, TMPRSS11D, TMPRSS11E, and TMPRSS11F, but only limited activity for TMPRSS11A and TMPRSS11B. By contrast, another recently presented work suggests that TMPRSS11A might process SARS-CoV-2 spike protein even more efficiently than TMPRSS2, at least in vitro ( 97 ). This is in line with previous reports on the activator activity of these MASPs: TMPRSS11A had been shown to activate MERS spike protein as well as hemagglutinin ( 64 ), TMPRSS11D primes SARS-CoV S protein for membrane fusion and also cleaves ACE2 ( 3 , 98 ), while TMPRSS11E had been reported as an activator of SARS and MERS coronaviruses ( 95 ).…”

Posttranslational modifications of serine protease TMPRSS13 regulate zymogen activation, proteolytic activity, and cell surface localization

“…N-linked glycans serve various functional roles, including assisting in proper polypeptide folding, protein quality control, and protein solubility ( 39 , 41 , 42 ). Several TTSP family members are known to be glycosylated, including hepsin ( 43 , 44 ), enteropeptidase ( 45 , 46 ), matriptase ( 47 , 48 ), matriptase-2 ( 49 ), corin ( 42 , 46 , 50 , 51 ), TMPRSS11a ( 52 ), and TMPRSS3 ( 53 ), where glycosylation is important for one or more processes including zymogen activation, catalytic activity, stability, trafficking to the cell surface, and shedding. The function of posttranslational modifications for individual proteases, while frequently modulating similar processes, cannot be predicted since there is currently no known general pattern, and glycosylation can have differential effects on catalytic activity and cellular properties.…”