Modulation of host vacuolar H+-ATPase by Legionella pneumophila effectors

Li Xu, Purdue University

Abstract

Legionella pneumophila is an opportunistic intracellular pathogen responsible for Legionnaires' disease. During infection, this bacterium delivers a large cohort of protein effectors into the host cell using the Dot/Icm type IV secretion system. These effectors modulate various cellular processes to establish a specialized niche permissive for bacterial replication in phagocytes. Like many intravacuolar pathogens, after being internalized by professional phagocytes, L. pneumophila is able to inhibit the acidification of its phagosome, thus bypassing the lysosomal killing. However, the molecular strategies utilized by the bacterium to inhibit the phagosomal acidification are still unknown. In this study, we identified a novel L. pneumophila effector protein, termed SidK, which specifically targets host v-ATPase, the multi-subunit protein complex primarily responsible for organelle acidification in eukaryotic cells. SidK binding interferes with the ATP hydrolysis as well as the proton translocation activities of the v-ATPase in vitro. Moreover, macrophages loaded with SidK display defects in phagosomal acidification and lysosomal killing of non-pathogenic bacteria. Although SidK is able to inhibit the v-ATPase function, the sidK deletion mutant shows no defect in intracellular growth. This is probably due to the presence of additional effectors with similar function. Further study led to the identification of two more Legionella effectors that target the v-ATPase, AnkB and LubX, which binds to the B and A subunit of the v-ATPase, respectively. Both effectors are involved in the host ubiquitination pathway. In vitro ubiquitination assay showed that the v-ATPase is ubiquitinated by LubX. In addition, our data suggest that L. pneumophila encodes previously unidentified protein(s) with eukaryotic E3 ligase activity. Taken together, our studies demonstrate that Legionella pneumophila is able to block phagosome acidification by subverting the function of host v-ATPase using multiple strategies.

Degree

Ph.D.

Advisors

Luo, Purdue University.

Subject Area

Biology|Microbiology|Virology

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