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Proteomic analysis of the secretome of Leishmania donovani

J Maxwell Silverman123, Simon K Chan456, Dale P Robinson27, Dennis M Dwyer6, Devki Nandan12, Leonard J Foster27 and Neil E Reiner123*

Author Affiliations

1 Department of Medicine (Division of Infectious Diseases), University of British Columbia, Faculty of Medicine, 2733 Heather St, Vancouver, British Columbia, V5Z 3J5, Canada

2 Vancouver Coastal Health Research Institute, 2647 Willow St. Vancouver, British Columbia, V5Z 3P1, Canada

3 Department Microbiology and Immunology, University of British Columbia, Faculty of Science, 2350 Health Sciences Mall, Vancouver, British Columbia, V6T 1Z3, Canada

4 Canada's Michael Smith Genome Sciences Centre, 570 West 7th Ave - Suite 100, Vancouver, British Columbia, V5Z 4S6, Canada

5 Bioinformatics Graduate Program, University of British Columbia, 100-570 West 7th Avenue, Vancouver, British Columbia, V5Z 4S6 Canada

6 Laboratory of Parasitic Diseases, Division of Intramural Research, NIAID, National Institutes of Health, 4 Center Drive, Bethesda, Maryland, 20892, USA

7 Department of Biochemistry and Molecular Biology, University of British Columbia, Faculty of Science, 2350 Health Sciences Mall, Vancouver, British Columbia, V6T 1Z3, Canada

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Genome Biology 2008, 9:R35  doi:10.1186/gb-2008-9-2-r35

Published: 18 February 2008

Abstract

Background

Leishmania and other intracellular pathogens have evolved strategies that support invasion and persistence within host target cells. In some cases the underlying mechanisms involve the export of virulence factors into the host cell cytosol. Previous work from our laboratory identified one such candidate leishmania effector, namely elongation factor-1α, to be present in conditioned medium of infectious leishmania as well as within macrophage cytosol after infection. To investigate secretion of potential effectors more broadly, we used quantitative mass spectrometry to analyze the protein content of conditioned medium collected from cultures of stationary-phase promastigotes of Leishmania donovani, an agent of visceral leishmaniasis.

Results

Analysis of leishmania conditioned medium resulted in the identification of 151 proteins apparently secreted by L. donovani. Ratios reflecting the relative amounts of each leishmania protein secreted, as compared to that remaining cell associated, revealed a hierarchy of protein secretion, with some proteins secreted to a greater extent than others. Comparison with an in silico approach defining proteins potentially exported along the classic eukaryotic secretion pathway suggested that few leishmania proteins are targeted for export using a classic eukaryotic amino-terminal secretion signal peptide. Unexpectedly, a large majority of known eukaryotic exosomal proteins was detected in leishmania conditioned medium, suggesting a vesicle-based secretion system.

Conclusion

This analysis shows that protein secretion by L. donovani is a heterogeneous process that is unlikely to be determined by a classical amino-terminal secretion signal. As an alternative, L. donovani appears to use multiple nonclassical secretion pathways, including the release of exosome-like microvesicles.