Synthetic peptides derived from fibrinogen and fibronectin change the conformation of purified platelet glycoprotein IIb-IIIa

J Biol Chem. 1987 Sep 15;262(26):12597-602.

Abstract

The glycoprotein IIb-IIIa complex (GP IIb-IIIa) is a platelet cell-surface receptor for fibrinogen and fibronectin. A carboxyl-terminal decapeptide of the fibrinogen gamma-chain (Leu-Gly-Gly-Ala-Lys-Gln-Ala-Gly-Asp-Val LGGAKQAGDV] and a tetrapeptide (Arg-Gly-Asp-Ser (RGDS] from the fibrinogen alpha-chain and the fibronectin cell-binding domain appear to mediate the binding of these ligands to GP IIb-IIIa. The present study was designed to examine the effects of these and related peptides on the structure of purified platelet GP IIb-IIIa. Treatment of GP IIb-IIIa with various synthetic peptides affected the glycoprotein so that GP IIb alpha became a substrate for hydrolysis by thrombin. The order of potency of these peptides was as follows: RGDS greater than LGGAKQAGDV greater than KGDS greater than RGES. This is the same order of potency in which these peptides inhibit fibrinogen binding to platelets. This effect was time-, temperature-, and concentration-dependent; RGDS induced a half-maximal effect at approximately 60 microM. In addition, RGDS, but not RGES, decreased the intensity of the intrinsic protein fluorescence of GP IIb-IIIa. Finally, the decapeptide or RGDS decreased the sedimentation coefficient of GP IIb-IIIa from 8.5 to 7.7 or 7.4 S, respectively, whereas RGES had a minimal effect. This decrease was accompanied by an increase in the Stoke's radius from 74 to 82 A with RGDS or 85 A with the decapeptide, indicating a peptide-induced unfolding of the GP IIb-IIIa complex. This change in conformation may be related to changes in the distribution and function of GP IIb-IIIa on the platelet surface that occur when adhesive proteins or peptides from the GP IIb-IIIa binding domains of these proteins bind to GP IIb-IIIa.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Binding Sites
  • Fibrin Fibrinogen Degradation Products / metabolism*
  • Fibronectins / metabolism*
  • Humans
  • Peptide Fragments / chemical synthesis
  • Peptide Fragments / pharmacology*
  • Platelet Aggregation
  • Platelet Membrane Glycoproteins / drug effects
  • Platelet Membrane Glycoproteins / metabolism*
  • Protein Binding
  • Protein Conformation / drug effects
  • Receptors, Fibronectin
  • Receptors, Immunologic / drug effects
  • Receptors, Immunologic / metabolism*
  • Thrombin / metabolism

Substances

  • Fibrin Fibrinogen Degradation Products
  • Fibronectins
  • Peptide Fragments
  • Platelet Membrane Glycoproteins
  • Receptors, Fibronectin
  • Receptors, Immunologic
  • Thrombin