title: Synthetic peptides derived from fibrinogen and fibronectin change the conformation of purified platelet glycoprotein IIb-IIIa.
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.
mesh_terms: D001665:Binding Sites; D005338:Fibrin Fibrinogen Degradation Products / Q000378:metabolism*; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000494:pharmacology*; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation / Q000187:drug effects; D017469:Receptors, Fibronectin; D011971:Receptors, Immunologic / Q000187:drug effects / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; D005353:Fibronectins; D010446:Peptide Fragments; D010980:Platelet Membrane Glycoproteins; D017469:Receptors, Fibronectin; D011971:Receptors, Immunologic; D013917:Thrombin