The peptide LSARLAF causes platelet secretion and aggregation by directly activating the integrin alpha(IIb)beta(3)

A novel peptide (designed to bind to alpha(IIb)beta(3)) caused platelet aggregation and aggregation-independent secretion of the contents of alpha-granules in an alpha(IIb)beta(3)-dependent fashion. The agonist peptide induced secretion in the presence of prostaglandin E-1. In cell-free assays, alpha(IIb)beta(3) bound specifically to immobilized agonist peptide and the peptide enhanced the binding of fibrinogen to immobilized alpha(IIb)beta(3). The agonist peptide apparently activates alpha(IIb)beta(3) by directly inducing a conformational change in the receptor. This change activates the platelets and causes secretion in a manner independent of fibrinogen binding.