Structure-function relationships in the activation of platelet thrombin receptors by receptor-derived peptides.

摘要: According to present models, thrombin activates platelets by cleaving its receptors after Arg41, creating a new N terminus which acts as tethered ligand. In support of this model, peptide (SFLLRNPNDKYEPF or TRP42/55) corresponding residues 42-55 has been shown activate the receptor. studies, structural basis for receptor activation was examined using fragments peptide, well variants with selected amino acid substitutions. The results show that features SFLLRNPNDKYEPF required mimic effects reside within first 6 residues, SFLLRN. A hexapeptide comprised these approximately 5 times more potent than parent in assays platelet aggregation and, addition, caused tyrosine phosphorylation, inhibition cAMP formation, and an increase cytosolic Ca2+. Omission either Ser residue Arg Asn greatly diminished activity, did substitution Ala Phe Arg. Substitution initial Leu, on other hand, had little adverse effect. inactive peptides SALLRN NPNDKYEPF no effect initiated SFLLRN, but FLLRN inhibited response both SFLLRN thrombin. These suggest are particularly important must be preceded another acid, identity is not tightly constrained. This observation comparisons homologous domains proteins whose tertiary structure known were used predict conformation SFLLR sequence. model emerged suggests domain may part extended beta intact cleavage causes it contract assume modified helical configuration. predicted side chains point same direction, potentially into pocket formed remainder