This Article Full Text (PDF) Other Versions of this Article: AEM.01944-07v1 74/3/753    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rossier, O. Articles by Cianciotto, N. P. Search for Related Content PubMed PubMed Citation Articles by Rossier, O. Articles by Cianciotto, N. P. Agricola Articles by Rossier, O. Articles by Cianciotto, N. P.

 Previous Article  |  Next Article 

Appl. Environ. Microbiol. doi:10.1128/AEM.01944-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The Type II Secretion System of Legionella pneumophila Elaborates Two Aminopeptidases as well as a Metalloprotease That Contributes to Differential Infection Among Protozoan Hosts

Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, IL 60611

^* To whom correspondence should be addressed. Email: n-cianciotto{at}northwestern.edu.

	Abstract

Legionella pneumophila, the agent of Legionnaires' disease, is an intracellular parasite of aquatic amoebae and human macrophages. A key factor for L. pneumophila in intracellular infection is its type II protein secretion system (Lsp). In order to more completely define Lsp output, we recently performed a proteomic analysis of culture supernatants. Based upon the predictions of that analysis, we have now found that L. pneumophila secretes two distinct aminopeptidase activities encoded by the genes lapA and lapB. Whereas lapA conferred activity against leucine-, phenylalanine- and tyrosine-aminopeptides, lapB was linked to the cleavage of lysine- and arginine-containing substrates. To assess the role of secreted aminopeptidases in intracellular infection, we examined the relative ability of lapA and lapB mutants to infect human U937 cell macrophages as well as Hartmannella and Acanthamoeba amoebae. Although these experiments identified a dispensable role for LapA and LapB, they uncovered a previously unrecognized role for the type II-dependent ProA (MspA) metalloprotease. Whereas proA mutants were not defective for macrophage or A. castellanii infection, they (but not their complemented derivatives) were impaired for growth upon co-culture with H. vermiformis. Thus, ProA represents the first type II effector implicated in an intracellular infection event. Furthermore, proA represents a L. pneumophila gene that shows differential importance amongst protozoan infection models, suggesting that the legionellae might have evolved some of its factors to especially target certain of its protozoan hosts.

This article has been cited by other articles:

• Soderberg, M. A., Dao, J., Starkenburg, S. R., Cianciotto, N. P. (2008). Importance of Type II Secretion for Survival of Legionella pneumophila in Tap Water and in Amoebae at Low Temperatures. Appl. Environ. Microbiol. 74: 5583-5588 [Abstract] [Full Text]