Implication of prokaryotic Rab-GTPases in pathogenesis and disease – ProRab

Pathogens that are able to enter and multiply within human cells are responsible for a large disease burden worldwide. Legionella pneumophila and Legionella longbeachae the causative agents of a severe pneumonia called Legionnaires’ disease are belonging to these intracellular bacterial pathogens. They are a considerable burden for public health due to sporadic and epidemic outbreaks and nosocomial infections (mortality rate 5-20% and up to 30% in hospital acquired infections), but they are also an economic problem due to the surveillance measurements that need to be taken to ensure that artificial water supply systems are not contaminated with Legionella. Thus we need to improve our knowledge of the biology of Legionella, of the factors important for the pathogenesis and their mechanisms of action, in order to design novel approaches for better diagnosis, surveillance and risk prediction.

In this project two teams with complementary expertise propose to combine their different strengths to investigate L. longbeachae host-pathogen interactions to elucidate mechanisms by which this human pathogen establishes a protective vacuole to replicate inside the eukaryotic host cell. Indeed, many studies on L. pneumophila species established that after internalization by host cells, intracellular Legionella avoids host cell degradation and multiplies in a distinct compartment named Legionella containing vacuole (LCV). The LCV recruits vesicles from the host secretory pathway and thereby transforms itself into an endoplasmic reticulum (ER)- like organelle where Legionella can multiply and differentiate. This is done partly by targeting host Rab GTPases, proteins central to the organization and dynamics of the cellular endomembrane system. Indeed, it has been shown that many of the secreted virulence factors of L. pneumophila like SidM/DrrA, SidD, LidA, LepB, Lem3 and AnkX, subvert Rab1 function, a GTPase involved in the regulation of ER-Golgi vesicular traffic. Surprisingly, our genome sequence analyses uncovered that most of these factors are not conserved in L. longbeachae. Thus it is not known how and whether this pathogenic species targets Rab proteins to establish its protective vacuole.

Intriguingly, L. longbeachae encodes many so-called “eukaryotic like proteins” that were to date only identified in eukaryotic organisms or very rarely identified in prokaryotic organisms. Among those proteins we identified the first prokaryotic Rab GTPase like protein (RabL). Thus, we hypothesise that L. longbeachae is secreting this protein into the host cell, where it acts like a eukaryotic Rab GTPase to interfere with vesicle trafficking and to establish a protective LCV where it can “safely” replicate to high numbers and thus cause disease. Here we propose to challenge our hypothesis and to analyze the molecular, biochemical and cellular functions of this Rab GTPase encoded by L. longbeachae, to understand how it acts in the host cell. This is an innovative project that will enable not only the identification of novel virulence strategies of Legionella but it will also increase our understanding of host processes implicated in disease progression, which may allow the identification of new targets for therapeutics.