Aggretin, a heterodimeric C-type lectin from Calloselasma rhodostoma (Malayan pit viper), stimulates platelets by binding to α2β1 integrin and glycoprotein Ib, activating Syk and phospholipase Cγ 2, but does not involve the glycoprotein VI/Fc receptor γ chain collagen receptor.
Aggretin, a potent platelet activator, was isolated from Calloselasma rhodostoma venom, and 30-amino acid N-terminal sequences of both subunits were determined. Aggretin belongs to the heterodimeric snake C-type lectin family and is thought to activate platelets by binding to platelet glycoprotein alpha(2)beta(1). We now show that binding to glycoprotein (GP) Ib is also required. Aggretin-induced platelet activation was inhibited by a monoclonal antibody to GPIb as well as by antibodies to alpha(2)beta(1). Binding of both of these platelet receptors to aggretin was confirmed by affinity chromatography. No binding of other major platelet membrane glycoproteins, in particular GPVI, to aggretin was detected. Aggretin also activates platelets from Fc receptor gamma chain (Fcgamma)-deficient mice to a greater extent than those from normal control mice, showing that it does not use the GPVI/Fcgamma pathway. Platelets from Fcgamma-deficient mice expressed fibrinogen receptors normally in response to collagen, although they did not aggregate, indicating that these platelets may partly compensate via other receptors including alpha(2)beta(1) or GPIb for the lack of the Fcgamma pathway. Signaling by aggretin involves a dose-dependent lag phase followed by rapid tyrosine phosphorylation of a number of proteins. Among these are p72(SYK), p125(FAK), and PLCgamma2, whereas, in comparison with collagen and convulxin, the Fcgamma subunit neither is phosphorylated nor coprecipitates with p72(SYK). This supports an independent, GPIb- and integrin-based pathway for activation of p72(SYK) not involving the Fcgamma receptor.
Navdaev
A
A
Theodor Kocher Institute, University of Berne, Freiestrasse 1, CH-3012 Berne, Switzerland.
Clemetson
J M
JM
Polgar
J
J
Kehrel
B E
BE
Glauner
M
M
Magnenat
E
E
Wells
T N
TN
Clemetson
K J
KJ
D017836:Agkistrodon; D000595:Amino Acid Sequence; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D002846:Chromatography, Affinity; D003094:Collagen / Q000494:pharmacology; D003435:Crotalid Venoms / Q000494:pharmacology; D004792:Enzyme Precursors / Q000097:blood*; D006801:Humans; D066298:In Vitro Techniques; D016023:Integrins / Q000097:blood* / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000097:blood*; D037102:Lectins / Q000737:chemistry / Q000494:pharmacology*; D037181:Lectins, C-Type; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D051966:Phospholipase C gamma; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000097:blood; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000187:drug effects / Q000502:physiology*; D021122:Protein Subunits; D011505:Protein-Tyrosine Kinases / Q000097:blood*; D038981:Receptors, Collagen; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D000072377:Syk Kinase; D010738:Type C Phospholipases / Q000097:blood*; D014757:Viper Venoms / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*
D003435:Crotalid Venoms; D004792:Enzyme Precursors; D016023:Integrins; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D037102:Lectins; D037181:Lectins, C-Type; D019038:Platelet Glycoprotein GPIb-IX Complex; D021122:Protein Subunits; D038981:Receptors, Collagen; D014757:Viper Venoms; C112292:rhodocytin protein, Calloselasma rhodostoma; D019000:Phosphotyrosine; C028890:convulxin; D003094:Collagen; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D010738:Type C Phospholipases; D051966:Phospholipase C gamma