title: Characterization of a novel protein from Proatheris superciliaris venom: proatherocytin, a 34-kDa platelet receptor PAR1 agonist.
abstract: Many toxins from viperid venoms have been characterised as powerful activators of platelets. Here, the venom from the East African Lowland viper, Proatheris superciliaris, was investigated for its effect on platelets and the coagulation system. Whole P. superciliaris venom stimulated platelet shape change and aggregation; however, the stimulation of platelet activation was unaffected by the structurally distinct Src family kinase inhibitors PP1 and PD0173952, suggesting that platelet activation was mediated by a G protein-coupled receptor. A platelet reactive 34-kDa protein was isolated from P. superciliaris venom which we have designated proatherocytin. This protein induced Src kinase-independent aggregation of both human and mouse platelets that was inhibited by the serine protease inhibitor AEBSF. Proatherocytin did not clot bovine or human fibrinogen, degrade fibrinogen or hydrolyse the serine protease substrate benzoyl-FVR-pNA. It activated human PAR1 on stably transfected rat kidney epithelial cells, whereas no activation of the trypsin receptor PAR2 was shown. Surprisingly, Edman degradation of proatherocytin revealed sequence identity with existing disintegrin-like domains of snake venom metalloproteinases. These results suggest that proatherocytin is a highly selective PAR1 agonist that also causes mouse platelet aggregation, probably through cleavage of PAR4.
authors.affiliation: Alistair Reid Venom Research Unit, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK. gavin.laing@liv.ac.uk
authors.forename: Gavin D
authors.initials: GD
authors.lastname: Laing
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Compton
authors.forename: Rithwik
authors.initials: R
authors.lastname: Ramachandran
authors.forename: Gemma L J
authors.initials: GL
authors.lastname: Fuller
authors.forename: Mark C
authors.initials: MC
authors.lastname: Wilkinson
authors.forename: Simon C
authors.initials: SC
authors.lastname: Wagstaff
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Watson
authors.forename: Aura S
authors.initials: AS
authors.lastname: Kamiguti
authors.forename: R David G
authors.initials: RD
authors.lastname: Theakston
authors.forename: Yotis A
authors.initials: YA
authors.lastname: Senis
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001777:Blood Coagulation / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects*; D020013:Calcium Signaling / Q000187:drug effects; D003124:Colorimetry; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006470:Hemorrhage / Q000097:blood / Q000139:chemically induced; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010974:Platelet Aggregation / Q000187:drug effects; D051381:Rats; D044463:Receptor, PAR-1 / Q000819:agonists* / Q000096:biosynthesis / Q000235:genetics; D012697:Serine Endopeptidases / Q000097:blood; D014757:Viper Venoms / Q000737:chemistry* / Q000494:pharmacology; D019061:src-Family Kinases / Q000037:antagonists & inhibitors
chemical_list: D044463:Receptor, PAR-1; D014757:Viper Venoms; C507615:proatherocytin protein, Proatheris superciliaris; D019061:src-Family Kinases; D012697:Serine Endopeptidases