title: Activation of a membrane-bound serine protease matriptase on the cell surface.
abstract: Matriptase is a type II transmembrane serine protease. The activation (i.e. conversion of the single-chain pro-form to the disulphide-linked-two-chain active form) of this enzyme is known to occur via a mechanism requiring its catalytic triad. We reported previously that the activated enzyme was produced in the conditioned medium when full-length rat matriptase was expressed in monkey kidney COS-1 cells. The present study aimed to address when and where the matriptase activation occurs. COS-1 cells expressing matriptase were labelled with a membrane-impermeable biotin derivative and then solubilized with Triton. Both activated and non-activated matriptase molecules were detected in the avidin precipitants of Triton extracts, whereas only the non-activated molecules were detected in the flow-through fraction of avidin-precipitation procedure. Single-chain matriptase has been thought to have an inherent activity. Indeed, a secreted single-chain variant of recombinant matriptase bearing mutation at the activation-cleavage site was found to exhibit the activity in hydrolyzing a synthetic peptide substrate at pH 7.5. However, the variant had little activity at pH 5.5, as found in the lumen of post-Golgi secretory vesicles. Altogether, it is concluded that the activation of matriptase may occur when the enzyme reaches the cell surface.
authors.affiliation: Kyoto University, Sakyo-ku, Kyoto City, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Miyake
authors.forename: Makoto
authors.initials: M
authors.lastname: Yasumoto
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tsuzuki
authors.forename: Tohru
authors.initials: T
authors.lastname: Fushiki
authors.forename: Kuniyo
authors.initials: K
authors.lastname: Inouye
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002462:Cell Membrane / Q000201:enzymology*; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D051381:Rats; D012697:Serine Endopeptidases / Q000378:metabolism*
chemical_list: D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C504592:Spint1 protein, rat; D012697:Serine Endopeptidases; C485595:matriptase