Characterization of three alboaggregins purified from Trimeresurus albolabris venom.
Alboaggregins (AL-A, AL-B, AL-C) isolated from Trimeresurus albolabris snake venom represent a new family of proteins which bind to platelet glycoprotein Ib (GPIb). These alboaggregins were purified to homogeneity with ion exchange HPLC (Mono-Q column) and hydrophobic HPLC (TSK Phenyl-5PW column). On SDS-polyacrylamide gel electrophoresis, apparent molecular weights of AL-A, AL-B and AL-C were 52 kDa, 26 kDa, and 121 kDa respectively, under nonreducing conditions. Upon reduction, each alboaggregin showed two types of chains with apparent molecular weights in the range of 15-20 kDa. All three alboaggregins agglutinated formalin-fixed platelets. Agglutination activities and binding of labeled alboaggregins to GPIb were specifically inhibited by the monoclonal antibody AK2 which is directed against the 45 kDa N-terminal region on GPIb, but not by monoclonal antibodies against other epitopes on GPIb. 125I-alboaggregin binding to platelets was not altered by the presence of thrombin. Alboaggregins did not bind to GPIIb/IIIa. Alboaggregins were competitive inhibitors for 125I-bovine vWF binding to platelets. Mutual competition studies between AL-A, AL-B and AL-C for the binding of labeled bovine vWF and AL-B to platelets demonstrated that AL-B and AL-C had a significantly higher affinity than AL-A.
Peng
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Department of Biochemistry, Temple University, School of Medicine, Philadelphia, PA 19140.
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Kirby
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D000371:Agglutination; D000911:Antibodies, Monoclonal / Q000276:immunology; D001667:Binding, Competitive / Q000502:physiology; D003435:Crotalid Venoms / Q000032:analysis*; D006801:Humans; D007457:Iodine Radioisotopes; D008970:Molecular Weight; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry / Q000302:isolation & purification*; D014841:von Willebrand Factor / Q000378:metabolism
D000911:Antibodies, Monoclonal; D003435:Crotalid Venoms; D007457:Iodine Radioisotopes; D010980:Platelet Membrane Glycoproteins; D011506:Proteins; C029748:Trimeresurus venoms; D014841:von Willebrand Factor