Matriptase is a type II transmembrane serine protease containing two complement proteases C1r/C1surchin embryonic growth factorbone morphogenetic protein domains (CUB repeat) and four low-density lipoprotein receptor class A domains (LDLRA repeat). The single-chain zymogen of matriptase has been found to exhibit substantial protease activity, possibly causing its own activation (i.e. conversion to a disulfide-linked two-chain fully active form), although the activation seems to be mediated predominantly by two-chain molecules. Our aim was to assess the roles of CUB and LDLRA repeats in zymogen activation. Transient expression studies of soluble truncated constructs of recombinant matriptase in COS-1 cells showed that the CUB repeat had an inhibitory effect on zymogen activation, possibly because it facilitated the interaction of two-chain molecules with a matriptase inhibitor, hepatocyte growth factor activator inhibitor type-1. By contrast, the LDLRA repeat had a promoting effect on zymogen activation. The effect of the LDLRA repeat seems to reflect its ability to increase zymogen activity. The proteolytic activities were higher in pseudozymogen forms of recombinant matriptase containing the LDLRA repeat than in a pseudozymogen without the repeat. Our findings provide new insights into the roles of these non-catalytic domains in the generation of active matriptase.Keywords: CUB repeat/hepatocyte growth factor activator inhibitor type-1/LDLRA repeat/matriptase/ zymogen activation.Abbreviations: Ac-KTKQLR-MCA, acetyl-L-LysLThrL-LysL-GlnL-LeuL-Arg4-methyl-coumaryl-7-amide; COS, CV-1 in origin and carrying the SV40 genetic material; CUB, complement proteases C1r/C1surchin embryonic growth factorbone morphogenetic protein; HAI-1, hepatocyte growth factor activator inhibitor type-1; HGF, hepatocyte growth factor; HRP, horseradish peroxidase; LDLRA, low-density lipoprotein receptor class A MWCO, molecular weight cut-off; r-EK, recombinant enteropeptidase; SEA, sea urchin sperm proteinenteropeptidaseagrin; SPCD, serine protease catalytic domain; WT, wild-type.Matriptase is a member of the type II transmembrane serine protease group, which is characterized by the presence of an N-terminal cytoplasmic domain followed by a signal-anchor transmembrane domain and an extracellular domain, including a C-terminal serine protease catalytic domain (SPCD) (Fig. 1) (16). Matriptase is first synthesized as a zymogen comprising 855 amino acid residues in human, mouse and rat enzymes. The matriptase zymogen undergoes cleavage between Arg614 and Val615 (activation cleavage), and the disulfide-linked two-chain fully active enzyme is generated (Fig. 1) (16). Two-chain matriptase exhibits activity with trypsin-like specificity and can cleave and activate a number of proteins, including pro-hepatocyte growth factor (HGF) and the precursor of a membrane-bound serine protease, prostasin (79). The potential substrates, abundant expression in the epithelial cells and keratinocytes and characteristic phenotypes in matriptase gene-disrupted mic...
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