Glycoproteins V and Ib-IX form a noncovalent complex in the platelet membrane

J Biol Chem. 1992 Jan 5;267(1):364-9.

Abstract

Platelet glycoprotein (GP) V is a Mr 82,000 plasma membrane protein of unknown function that is cleaved by the potent platelet agonist, thrombin, to yield a Mr 69,500 fragment (GPVf1). Platelet GPIb, a disulfide-linked alpha beta heterodimer (Mr 160,000) that forms a noncovalent complex with GPIX (Mr 22,000), functions as the platelet adhesion receptor for surface-bound von Willebrand factor. Association between GPV and GPIb-IX has been suggested by the finding that both proteins are deficient in the Bernard-Soulier syndrome, a bleeding disorder characterized by giant platelets and defective interaction with von Willebrand factor. Here we report that GPV and GPIb-IX are coprecipitated by monoclonal antibodies (mAbs) against GPV, GPIb, or GPIX when platelets are solubilized in the mild detergent, digitonin. Treatment of digitonin immunopreciptates with the nonionic detergent, Nonidet P-40, released GPV from anti-GPIb and anti-GPIX mAb precipitates and GPIb-IX from the anti-GPV mAb precipitate. Removal of the Mr 45,000 amino-terminal part of GPIb alpha by treatment with elastase did not abrogate association of GPV with GPIb-IX, showing that the leucine-rich repeat sequences in GPIb alpha are not required for complex formation. Binding studies with 125I-labeled mAbs showed the presence of 24,370 GPIb-IX complexes and 11,170 molecules of GPV/platelet (n = 5). These data show that the leucine-rich glycoproteins GPV and GPIb-IX form a noncovalent complex in the platelet membrane. GPV may play a role in the interaction of platelets with von Willebrand factor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / immunology
  • Blood Platelets / drug effects
  • Blood Platelets / metabolism*
  • Cell Membrane / metabolism
  • Detergents
  • Digitonin / pharmacology
  • Electrophoresis, Polyacrylamide Gel
  • Humans
  • Mice
  • Mice, Inbred BALB C
  • Octoxynol
  • Platelet Aggregation
  • Platelet Membrane Glycoproteins / immunology
  • Platelet Membrane Glycoproteins / metabolism*
  • Polyethylene Glycols
  • Precipitin Tests

Substances

  • Antibodies, Monoclonal
  • Detergents
  • Platelet Membrane Glycoproteins
  • Polyethylene Glycols
  • Octoxynol
  • Nonidet P-40
  • Digitonin