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Eukaryotic Cell doi:10.1128/EC.00073-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Internal and surface-localized MSP of Leishmania and their differential release from promastigotes

Departments of Internal Medicine, Biochemistry, Microbiology, and Epidemiology, Program in Molecular Biology, University of Iowa, Iowa City, IA 52242; VA Medical Center, Iowa City, IA 52246

^* To whom correspondence should be addressed. Email: chaoqun-yao{at}uiowa.edu.

	Abstract

MSP (major surface protease), also called GP63, is a virulence factor of Leishmania spp. protozoa. There are three pools of MSP, located either internally within the parasite, anchored to the surface membrane, or released into the extracellular environment. The regulation and biological functions of these MSP pools are unknown. Herein we investigated the trafficking and extrusion of surface versus internal MSPs. Virulent L. chagasi undergo a growth-associated lengthening in the T of surface-localized MSP, but this did not occur in the attenuated L5 strain. The release of surface-localized MSP was enhanced in a dose-dependent manner by MCD, which chelates membrane cholesterol/ergosterol. Furthermore, incubation of promastigotes at 37^oC with Matrigel^TM matrix, a soluble basement membrane extract of EHS tumor cells, stimulated release of internal MSP but not surface-located MSP. Taken together, these data indicate that MSP subpopulations in distinct cellular locations are released from the parasite under different environmental conditions. We hypothesize that the internal MSP with its lengthy T does not serve as a pool for promastigote surface MSP in the sand fly vector, but that it instead functions as an MSP pool ready for a quick release upon inoculation of metacyclic promastigotes into mammals. We present a model in which these different MSP pools are released under distinct life cycle-specific conditions.