TMPRSS11A is a member of the HAT/DESC subfamily of TTSPs.  It is notably expressed in the respiratory system as well as on cell surfaces.  Additionally, it has been shown to facility the entry of the virus SARS-CoV-1 into human cells.  

TMRPSS11A

HAT, or TMPRS11D, is a member of the HAT/DESC subfamily of TTSPs.  It was initially discovered in the sputum of chronic respiratory disease patients, and it is thought to have a variety of physiological roles in epithelial tissue.  Proposed functions of this protease include:

- suppressing coagulation through fibrinogenolysis
- activating the protease activated receptor (PAR)-2
- influencing cell migration and adhesion via urokinase plasminogen activator cleavage

TMPRSS11D has been shown to activate the S protein of SARS-CoV-1 by cleaving it into its S1 and S2 subunits  This facilitates endosomal entry of the virus into a host human cell.  

HAT (TMPRSS11D)

The HAT/DESC subfamily of TTSPs is hallmarked by an identical stem region that has a single sea urchin sperm protein, enteropeptidase, agrin (SEA) domain as well as similar amino acid sequencing in all other domains.  Members include:

- DESC1 (encoded by TMPRSS11E)
- HAT (encoded by TMPRSS11D)
- HAT-like 4 (encoded by TMPRSS11F)
- HAT-like 5 (encoded by TMPRSS11B)
- TMPRSS11A (encoded by TMPRSS11A)

Michigan State University

Type II Transmembrane Serine Proteases (TTSPs) are a large family of serine proteases.  They can be further categorized based off of the amino acid sequence of their stem region, which exists between a transmembrane signal anchor and the serine protease domain, as well as the chromosomal location of their genes.  Subfamilies include:

- matriptase
- hepsin/transmembrane protease serine (hepsin/TMPRSS) 
- corin
- human airway trypsin-like protease/differentially expressed in squamous cell carcinoma (HAT/DESC)

Type II Transmembrane Serine Proteases (TTSPs) 

Sales, K. U., Hobson, J. P., Wagenaar-Miller, R., Szabo, R., Rasmussen, A. L., Bey, A., ... & Bugge, T. H. (2011). Expression and genetic loss of function analysis of the HAT/DESC cluster proteases TMPRSS11A and HAT. PLoS One, 6(8), e23261.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0023261
doi: 10.1371/journal.pone.0023261

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