title: Platelet receptor recognition site on human fibrinogen. Synthesis and structure-function relationship of peptides corresponding to the carboxy-terminal segment of the gamma chain.
abstract: Binding of fibrinogen to human platelets depends on the interaction of the gamma-chain carboxy-terminal segment with specific receptors exposed by different agonists such as ADP, epinephrine, and thrombin. The functions of a series of synthetic peptides encompassing the sequence of the 15 carboxy-terminal residues of the gamma chain were investigated in this study. Both pentadecapeptide (gamma 397-411) and dodecapeptide (gamma 400-411) inhibited binding of 125I-fibrinogen to ADP-treated platelets, with the concentration causing 50% inhibition (IC50) being 28 microM. In comparison, decapeptide (gamma 402-411) was almost 4 times less active (IC50 = 106 microM), thus suggesting that the two histidine residues (gamma 400-401) are required for a full inhibitory effect. A heptapeptide (gamma 405-411) had a similar effect (IC50 = 102 microM) whereas a pentapeptide (gamma 407-411) was even less inhibitory (IC50 = 190 microM), indicating that the lack of lysine (gamma 406) further diminishes the reactivity of the platelet recognition site on the gamma chain of human fibrinogen. The heptapeptide (gamma 400-406) containing two histidine residues and derived from the dodecapeptide by proteolytic degradation with trypsin had very low inhibitory activity. The synthetic peptides inhibited fibrinogen-supported platelet aggregation in the same order of decreasing reactivity: pentadecapeptide = dodecapeptide greater than decapeptide = heptapeptide greater than pentapeptide. Modified synthetic pentadecapeptides bearing tyrosine or cysteinyltyrosine at the amino terminal were prepared to provide a means for radiolabeling and for formation of molecules of higher valency.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D010446:Peptide Fragments / Q000032:analysis; D010455:Peptides / Q000138:chemical synthesis* / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D010446:Peptide Fragments; D010455:Peptides; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D005340:Fibrinogen