This entry represents transmembrane serine protease 9 (also known as polyserase-1) (), which belongs to MEROPS peptidase family S1A (clan PA(S)). It is encoded by the TMPRSS9 gene on chromosome 19p13 in Homo sapiens. This protein is synthesised as a membrane-associated polyprotein which undergoes post-translational cleavage to generate 3 independent serine protease chains (serase-1, serase-2 and serase-3); however it is unclear whether cleavage always takes place [, ]. The cleaved chains may remain attached to the membrane via disulphide bonds. Two of these products, serase-1 and serase-2, are proteolytically active against synthetic peptides commonly used for assaying serine proteases and their activities, and are blocked by serine protease inhibitors. However, serase-3 lacks the essential Ser residue of the catalytic triad at position 1009 and is predicted to be inactive. The domain architecture includes a type II transmembrane motif, a low-density lipoprotein receptor A domain, and three tandem trypsin-like serine protease domains [].
