Alboaggregin-B: a new platelet agonist that binds to platelet membrane glycoprotein Ib.
A new protein, called alboaggregin-B (AL-B), has been isolated from Trimeresurus albolabris venom by ion-exchange chromatography. It agglutinated platelets without the need for Ca2+ or any other cofactor. The purified protein showed an apparent molecular mass on SDS-PAGE and gel filtration of about 23 kDa under nonreducing conditions. Ristocetin did not alter the binding of AL-B to platelets or affect AL-B-induced platelet agglutination. Agglutinating activity was not dependent on either proteolytic or lectin-like activity in AL-B. Binding analysis showed that AL-B bound to platelets with high affinity (Kd = 13.6 +/- 9.3 nM) at approximately 30,800 +/- 14,300 binding sites per platelet. AL-B inhibited the binding of labeled bovine von Willebrand factor (vWF) to platelets. Monoclonal antibodies against the 45-kDa N-terminal domain of platelet glycoprotein Ib inhibited the binding both of AL-B and of bovine vWF to platelets, and also inhibited platelet agglutination induced by AL-B and bovine vWF. Specific removal of the N-terminal domain of GPIb by treatment of the platelets with elastase or Serratia marcescens protease reduced the binding of labeled AL-B and bovine vWF to platelets and blocked platelet agglutination caused by both agonists. Monoclonal antibodies to glycoprotein IIb/IIIa, to bovine vWF, and to bovine serum albumin did not show any effect on the binding of AL-B to platelets. Our results indicate that the binding domain for AL-B on platelet GPIb is close to or identical with the one for vWF. This new protein may be a very useful tool for studying the interaction between platelets and vWF.
Peng
M
M
Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
Lu
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Kirby
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D000911:Antibodies, Monoclonal / Q000502:physiology; D001667:Binding, Competitive / Q000187:drug effects; D003435:Crotalid Venoms / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D006384:Hemagglutination / Q000187:drug effects; D006801:Humans; D006868:Hydrolysis; D008666:Metalloendopeptidases / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins / Q000737:chemistry* / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D014841:von Willebrand Factor / Q000378:metabolism
D000911:Antibodies, Monoclonal; D003435:Crotalid Venoms; D010980:Platelet Membrane Glycoproteins; C029748:Trimeresurus venoms; D014841:von Willebrand Factor; D008666:Metalloendopeptidases; C044194:microbial metalloproteinases