Rhinocetin, a venom-derived integrin-specific antagonist inhibits collagen-induced platelet and endothelial cell functions.
Snaclecs are small non-enzymatic proteins present in viper venoms reported to modulate hemostasis of victims through effects on platelets, vascular endothelial, and smooth muscle cells. In this study, we have isolated and functionally characterized a snaclec that we named "rhinocetin" from the venom of West African gaboon viper, Bitis gabonica rhinoceros. Rhinocetin was shown to comprise α and β chains with the molecular masses of 13.5 and 13 kDa, respectively. Sequence and immunoblot analysis of rhinocetin confirmed this to be a novel snaclec. Rhinocetin inhibited collagen-stimulated activation of human platelets in a dose-dependent manner but displayed no inhibitory effects on glycoprotein VI (collagen receptor) selective agonist, CRP-XL-, ADP-, or thrombin-induced platelet activation. Rhinocetin antagonized the binding of monoclonal antibodies against the α2 subunit of integrin α2β1 to platelets and coimmunoprecipitation analysis confirmed integrin α2β1 as a target for this venom protein. Rhinocetin inhibited a range of collagen-induced platelet functions such as fibrinogen binding, calcium mobilization, granule secretion, aggregation, and thrombus formation. It also inhibited integrin α2β1-dependent functions of human endothelial cells. Together, our data suggest rhinocetin to be a modulator of integrin α2β1 function and thus may provide valuable insights into the role of this integrin in physiological and pathophysiological scenarios, including hemostasis, thrombosis, and envenomation.
Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading RG6 6UB, United Kingdom.
Sakthivel
S
Vaiyapuri
E Gail
EG
Hutchinson
Marfoua S
MS
Ali
Abeer
A
Dannoura
Ronald G
RG
Stanley
Robert A
RA
Harrison
Andrew B
AB
Bicknell
Jonathan M
JM
Gibbins
D000595:Amino Acid Sequence; D000818:Animals; D001777:Blood Coagulation / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects*; D020013:Calcium Signaling / Q000187:drug effects; D002448:Cell Adhesion; D002465:Cell Movement; D049109:Cell Proliferation; D002478:Cells, Cultured; D003094:Collagen / Q000502:physiology*; D042783:Endothelial Cells / Q000187:drug effects*; D006401:Hematologic Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects / Q000502:physiology; D006801:Humans; D038982:Integrin alpha2beta1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008969:Molecular Sequence Data; D010974:Platelet Aggregation / Q000187:drug effects; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D022142:Secretory Vesicles / Q000378:metabolism; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D014757:Viper Venoms / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D017819:Viperidae
D006401:Hematologic Agents; D038982:Integrin alpha2beta1; D014757:Viper Venoms; C575520:rhinocetin protein, Bitis gabonica rhinoceros; D003094:Collagen