Isolation of a Myoinhibitory Peptide fromLeishmania major(Kinetoplastida: Trypanosomatidae) and Its Function in the Vector Sand FlyPhlebotomus papatasi(Diptera: Psychodidae)

Abstract

Protozoan parasites in the genus Leishmania are ingested by sand flies with blood and multiply in the gut until they are transmitted to a vertebrate host when the sand fly blood feeds again. Infections of the enzootic vector Phlebotomus papatasi Scopoli result in distended midguts with no spontaneous gut contractions. Using a P. papatasi hindgut contraction bioassay, a paralytic factor sensitive to trypsin, chymotrypsin, proteinase-K, and heating at 56 degrees C was detected in crude lysates of Leishmania major promastigotes. Application of parasite lysate to isolated hindguts resulted in reversible, dose-dependent inhibition of spontaneous contractions. Mean volume of isolated midguts and hindguts increased by 50-60% after application of L. major lysate. L. major paralytic factor was purified 10(4)-fold over the total protein preparation and yielded a hydrophobic 12-kDa peptide. Myoinhibitory activity eluted as a single peak in reverse phase-high-pressure liquid chromatography. Tandem mass spectrometry resulted in 15 amino acid sequences, three of them sharing 45-73% homology with short hypothetical gene products of undefined function from Pseudomonas, Halobacterium, and Drosophila. This unique protozoan peptide mimics the function of endogenous insect neuropeptides that control visceral muscle contractions. By this novel mechanism, parasites persist in the expanded, relaxed midgut after blood meal and peritrophic matrix digestion. This allows time for development and migration of infective forms, facilitating sand fly vector competence and parasite transmission.