title: Selective tryptic cleavage at the tethered ligand site of the amino terminal domain of proteinase-activated receptor-2 in intact cells.
abstract: In intact cells, trypsin activates proteinase-activated receptor-2 (PAR(2)) by hydrolysis at residues R(36)/S(37) (amino acids are abbreviated by their one-letter code), revealing an active tethered ligand sequence. We sought to determine whether in intact cells, the tryptic cleavage/activation of PAR(2) might also be accompanied by hydrolysis at other potential N-terminal cleavage sites, like residues K(34), R(41), K(51), and K(72), as implied by the tryptic cleavage in vitro at these residues of Escherichia coli-expressed human N-terminal PAR(2)R(31)-P(79). To this end, four PAR(2) mutants with altered tryptic cleavage sites were prepared (PAR(2)R(36)A, PAR(2)S(37)P, PAR(2)R(41)A, and PAR(2)R(36)AR(41)A), expressed in Kirsten virus-transformed rat kidney cells and were evaluated together with the wild-type PAR(2)-expressing cells for 1) activation (Ca(2+) signaling) by trypsin and the receptor-activating peptide SLIGRL-NH(2) (SL-NH(2)) and 2) the tryptic release of two antigenic receptor determinants, one N-terminal to the R(36)/S(37) cleavage/activation site detected by SLAW-A antibody and the second (detected by antibody, B5), N-terminal to residues K(51), K(72). None of the mutants resistant to cleavage at R(36) were activated by trypsin, yet all retained reactivity to B5 and all were activated by SL-NH(2). In contrast, trypsin activated both wild-type and PAR(2)R(41)A, leading to a disappearance of SLAW-A but not B5 reactivity. We conclude that, as opposed to the E. coli-expressed PAR(2) N-terminal polypeptide, PAR(2) expressed in intact cells displays selective tryptic cleavage at the R(36)/S(37) activation site, without cleaving downstream. Thus, in intact cells, trypsin activation does not concurrently "disarm" rat PAR(2), but leaves the "tethered ligand" persistently attached to the body of the receptor.
authors.affiliation: Diabetes/Endocrine and Mucosal Inflammation Research Groups, Department of Pharmacology, University of Calgary Faculty of Medicine, Calgary, Alberta, Canada. alani@ucalgary.ca
authors.forename: Bahjat
authors.initials: B
authors.lastname: Al-Ani
authors.forename: Morley D
authors.initials: MD
authors.lastname: Hollenberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D005434:Flow Cytometry; D007150:Immunohistochemistry; D007668:Kidney / Q000166:cytology; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D051381:Rats; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014357:Trypsin / Q000378:metabolism*
chemical_list: D009842:Oligopeptides; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin; C112356:seryl-leucyl-isoleucyl-glycyl--arginyl-leucinamide; D014357:Trypsin