Interaction of purified actin-binding protein with the platelet membrane glycoprotein Ib-IX complex.
The interaction of platelet membrane glycoprotein (GP) Ib-IX complex with the cytoplasmic membrane skeleton is potentially of major importance in regulating platelet function. Indirect evidence suggested that this interaction is mediated by actin-binding protein, but it is not known whether GP Ib-IX and actin-binding protein associate directly. To examine more closely the nature of this association, purified GP Ib-IX complex was specifically bound and oriented on the surface of impermeable polymer beads via a monoclonal antibody, AK 2, directed against the extracytoplasmic domain of GP Ib alpha (glycocalicin). Binding was specific since 1) it was abolished by excess unlabeled actin-binding protein; 2) there was no detectable specific binding of radiolabeled actin-binding protein to beads coated with glycocalicin, the major extracytoplasmic proteolytic fragment of GP Ib alpha; and 3) unlike actin-binding protein, there was no specific binding of bovine serum albumin or human platelet vinculin to the GP Ib-IX complex-coated beads. Binding of actin-binding protein to the GP Ib-IX complex-coated beads, but not to the glycocalicin-coated beads, was saturable and reversible (apparent Kd = 1 x 10(-7) M). These experiments provide direct evidence that actin-binding protein can bind to the cytoplasmic domain of a membrane glycoprotein. Because actin-binding protein is found submembranously in cells other than the platelet, it is possible that this protein may link actin filaments to the plasma membrane in those cells.
Andrews
R K
RK
Gladstone Foundation Laboratoires for Cardiovascular Disease, University of California, San Francisco 94140-0608.
Fox
J E
JE
D000199:Actins / Q000378:metabolism; D000911:Antibodies, Monoclonal; D001792:Blood Platelets / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000302:isolation & purification / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D010975:Platelet Aggregation Inhibitors / Q000378:metabolism; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D016596:Vinculin
D000199:Actins; D000911:Antibodies, Monoclonal; D003598:Cytoskeletal Proteins; D010975:Platelet Aggregation Inhibitors; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; C023592:glycocalicin; D016596:Vinculin