title: Human thrombin receptors are insensitive to thrombin-like snake venom enzymes.
abstract: Thrombin-like snake venoms enzymes, flavoxobin, and okinaxobin I isolated from Trimeresurus flavoviridis and Trimeresurus okinavensis, respectively, were examined in SH-EP cells and evaluated whether or not they can activate human thrombin receptors. Flavoxobin was almost completely inactive in both assays for phosphoinositide turnover and DNA synthesis. In contrast, okinaxobin I stimulated phosphoinositide turnover in a dose dependent manner, but considerably weakly. The EC50 value was about 100 nM, which was 4,000 times larger than that of alpha-thrombin. This stimulation was not inhibited by hirudin, an effective inhibitor of alpha-thrombin. Okinaxobin I also induced a very weak stimulation of DNA synthesis. These results suggest that thrombin-like snake venom enzymes interact with human thrombin receptors in inefficient ways. Weak interactions of the enzymes with thrombin receptor and inhibitor were ascribed to the incomplete formation of a lysine-cation cluster necessary for electrostatic molecular recognition.
authors.affiliation: Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Shimohigashi
authors.forename: T
authors.initials: T
authors.lastname: Nose
authors.forename: M
authors.initials: M
authors.lastname: Ohno
authors.forename: Y
authors.initials: Y
authors.lastname: Ogino
authors.forename: T
authors.initials: T
authors.lastname: Costa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D003435:Crotalid Venoms; D004247:DNA / Q000096:biosynthesis; D004261:DNA Replication / Q000187:drug effects; D005418:Flavodoxin / Q000494:pharmacology; D006629:Hirudins / Q000494:pharmacology; D006801:Humans; D008969:Molecular Sequence Data; D010716:Phosphatidylinositols / Q000378:metabolism; D018179:Receptors, Thrombin / Q000187:drug effects / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D013917:Thrombin / Q000494:pharmacology*; D017841:Trimeresurus
chemical_list: D003435:Crotalid Venoms; D005418:Flavodoxin; D006629:Hirudins; D010716:Phosphatidylinositols; D018179:Receptors, Thrombin; D004247:DNA; D012697:Serine Endopeptidases; C057255:flavoxobin; C068144:okinaxobin I; D013917:Thrombin