AN INHIBITOR OF COLLAGEN-INDUCED PLATELET-AGGREGATION FROM THE SALIVAOF TRIATOMA-PALLIDIPENNIS

The saliva of Triatoma pallidipennis, a blood-sucking triatomine bug ( Hemiptera, family Reduviidae, subfamily Triatominae) was found to cont ain a factor that specifically inhibits collagen-induced platelet aggr egation. The 19-kDa protein was purified to homogeneity and named pall idipin. Collagen-mediated aggregation of platelets in plasma and of wa shed platelets was inhibited with the same efficacy. No inhibition of aggregation stimulated by other effecters (ADP, thrombin, thromboxane A(2) mimetic U46619, phorbol ester) was detected. Pallidipin had no ef fect on platelet adhesion to collagen but inhibited ATP release from p latelets. It interacted reversibly with platelets and may share with c ollagen a common target on them. The protein exhibits a unique primary structure (predicted from cDNA clones) with no significant similarity to other previously described sequences. The protein produced in reco mbinant baby hamster kidney cells had antiaggregatory effects similar to those of native pallidipin. Availability of recombinant pallidipin will allow further investigation of the precise mechanism of action.