Role of botrocetin in platelet agglutination: formation of an activated complex of botrocetin and von Willebrand factor.
Botrocetin (venom coagglutinin) induces binding of von Willebrand factor (vWF) to platelet glycoprotein Ib (GPIb), resulting in platelet agglutination. A mechanism whereby botrocetin causes vWF to change to an active platelet-agglutinating form is proposed. Incubation of native vWF with botrocetin yielded an increasingly active vWF with slower migration in two-dimensional immunoelectrophoresis but with no apparent change in vWF multimer pattern. The "activated" vWF eluted mainly in the void volume (Vo) (Bio-Gel A-15m column chromatography). Botrocetin eluted in the included volume (Vi). Vo peaks appeared to contain a vWF-botrocetin complex, based on bioassays and immunoassays. 125I-Botrocetin mixed with vWF eluted in two peaks: in the Vo, coincident with active vWF, and in the Vi. With von Willebrand disease (vWD) plasma lacking vWF, 125I-Botrocetin eluted in the Vi only. It did not bind to platelets without vWF. In aggregometric studies, antibodies (Ab) against botrocetin, vWF, and GPIb prevented botrocetin-induced platelet agglutination and caused dissolution of preformed platelet agglutinates. Immunostaining of aggregates with antibotrocetin Ab revealed a positive reaction. Botrocetin appears to act in a two-step manner, first binding with vWF to form a complex, which then binds to GPIb to cause agglutination. All three components, vWF, botrocetin, and GPIb, appear to be required for maintenance of stable platelet agglutinates.
Read
M S
MS
Department of Pathology, University of North Carolina, Chapel Hill 27599.
Smith
S V
SV
Lamb
M A
MA
Brinkhous
K M
KM
D000818:Animals; D001780:Blood Coagulation Tests / Q000295:instrumentation; D001792:Blood Platelets / Q000032:analysis / Q000378:metabolism; D003435:Crotalid Venoms / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D007106:Immune Sera; D046911:Macromolecular Substances; D010974:Platelet Aggregation; D011817:Rabbits; D013194:Staining and Labeling; D014841:von Willebrand Factor / Q000276:immunology / Q000502:physiology*
D003435:Crotalid Venoms; D007106:Immune Sera; D046911:Macromolecular Substances; D014841:von Willebrand Factor; C030961:botrocetin