CHARACTERIZATION OF POLYMER RELEASE FROM THE FLAGELLAR POCKET OF LEISHMANIA-MEXICANA PROMASTIGOTES

Trypanosomatids contain a unique compartment, the flagellar pocket, fo rmed by an invagination of the plasma membrane at the base of the flag ellum, which is considered to be the sole cellular site for endocytosi s and exocytosis of macromolecules. The culture supernatant of Leishma nia mexicana promastigotes, the insect stage of this protozoan parasit e, contains two types of polymers: a filamentous acid phosphatase (sAP ) composed of a 100-kD phosphoglycoprotein with non-covalently associa ted proteo high molecular weight phosphoglycan (proteo-HMWPG) and fibr ous material termed network consisting of complex phosphoglycans. Secr etion of both polymers is investigated using mAbs and a combination of light and electron microscopic techniques. Long filaments of sAP are detectable in the lumen of the flagellar pocket. Both sAP filaments an d network material emerge from the ostium of the flagellar pocket. Whi le sAP filaments detach from the cells, the fibrous network frequently remains associated with the anterior end of the parasites and can be found in the center of cell aggregates. The related species L. major f orms similar networks. Since polymeric structures cannot be detected i n intracellular compartments, it is proposed that monomeric or, possib ly, oligomeric subunits synthesized in the cells are secreted into the flagellar pocket. Polymer formation from subunits is suggested to occ ur in the lumen of the pocket before release into the culture medium o r, naturally, into the gut of infected sandflies.