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 platele t 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 ce ll-free assays, alpha(IIb)beta(3) bound specifically to immobilized ag onist peptide and the peptide enhanced the binding of fibrinogen to im mobilized 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.