Computational modeling and experimental validation of the
            <i>Legionella</i>
            and
            <i>Coxiella</i>
            virulence-related type-IVB secretion signal

149

Successful macrophage colonization by Coxiella burnetii, the cause of human Q fever, requires pathogen-directed biogenesis of a large, growth-permissive parasitophorous vacuole (PV) with phagolysosomal characteristics. The vesicular trafficking pathways co-opted by C. burnetii for PV development are poorly defined; however, it is predicted that effector proteins delivered to the cytosol by a defective in organelle trafficking/intracellular multiplication (Dot/ Icm) type 4B secretion system are required for membrane recruitment. Here, we describe involvement of clathrin-mediated vesicular trafficking in PV generation and the engagement of this pathway by the C. burnetii type 4B secretion system substrate Coxiella vacuolar protein A (CvpA). CvpA contains multiple dileucine [DERQ]XXXL [LI] and tyrosine (YXXΦ)-based endocytic sorting motifs like those recognized by the clathrin adaptor protein (AP) complexes AP1, AP2, and AP3. A C. burnetii ΔcvpA mutant exhibited significant defects in replication and PV development, confirming the importance of CvpA in infection. Ectopically expressed mCherry-CvpA localized to tubular and vesicular domains of pericentrosomal recycling endosomes positive for Rab11 and transferrin receptor, and CvpA membrane interactions were lost upon mutation of endocytic sorting motifs. Consistent with CvpA engagement of the endocytic recycling system, ectopic expression reduced uptake of transferrin. In pull-down assays, peptides containing CvpA-sorting motifs and full-length CvpA interacted with AP2 subunits and clathrin heavy chain. Furthermore, depletion of AP2 or clathrin by siRNA treatment significantly inhibited C. burnetii replication. Thus, our results reveal the importance of clathrincoated vesicle trafficking in C. burnetii infection and define a role for CvpA in subverting these transport mechanisms.type IV secretion | vesicular fusion

Section: Significancementioning

confidence: 99%

“…To date, over 80 C. burnetii genes that encode T4BSS substrates have been identified (17)(18)(19)(20)(21)(22)(23). These substrates have largely been identified using L. pneumophila as a surrogate host and adenylate cyclase or β-lactamase-based translocation assays.…”

mentioning

confidence: 99%

Coxiella burnetii effector protein subverts clathrin-mediated vesicular trafficking for pathogen vacuole biogenesis

Larson

Beare

Howe

et al. 2013

149

“…S2D). cvpB encodes an 809-aa protein with a PmrA consensus sequence (18) 102 nt upstream of the start codon and a putative E-block domain (19) at the C terminus (SI Appendix, Fig. S2A).…”

Section: Identification Of Coxiella Factors Involved In CCV Biogenesimentioning

confidence: 99%

Coxiella burnetii effector CvpB modulates phosphoinositide metabolism for optimal vacuole development

Martínez

Allombert

Cantet

et al. 2016

129

The Q fever bacterium Coxiella burnetii replicates inside host cells within a large Coxiella-containing vacuole (CCV) whose biogenesis relies on the Dot/Icm-dependent secretion of bacterial effectors. Several membrane trafficking pathways contribute membranes, proteins, and lipids for CCV biogenesis. These include the endocytic and autophagy pathways, which are characterized by phosphatidylinositol 3-phosphate [PI(3)P]-positive membranes. Here we show that the C. burnetii secreted effector Coxiella vacuolar protein B (CvpB) binds PI(3)P and phosphatidylserine (PS) on CCVs and early endosomal compartments and perturbs the activity of the phosphatidylinositol 5-kinase PIKfyve to manipulate PI(3)P metabolism. CvpB association to early endosome triggers vacuolation and clustering, leading to the channeling of large PI(3)P-positive membranes to CCVs for vacuole expansion. At CCVs, CvpB binding to early endosome-and autophagy-derived PI(3)P and the concomitant inhibition of PIKfyve favor the association of the autophagosomal machinery to CCVs for optimal homotypic fusion of the Coxiella-containing compartments. The importance of manipulating PI(3)P metabolism is highlighted by mutations in cvpB resulting in a multivacuolar phenotype, rescuable by gene complementation, indicative of a defect in CCV biogenesis. Using the insect model Galleria mellonella, we demonstrate the in vivo relevance of defective CCV biogenesis by highlighting an attenuated virulence phenotype associated with cvpB mutations.Coxiella burnetii | host-pathogen interactions | phosphoinositides

“…Another feature of the LCV is enrichment of polyubiquitin conjugates around the vacuolar membrane (8). This sophisticated membrane remodeling process is achieved by the coordinated activity of effector proteins delivered into the host through the Dot/Icm apparatus (9,10). However, the mechanism underlying these processes is still not well established.…”

mentioning

confidence: 99%

The Legionella effector SidC defines a unique family of ubiquitin ligases important for bacterial phagosomal remodeling

Hsu

Luo

Qiu

et al. 2014

108

147

The activity of proteins delivered into host cells by the Dot/Icm injection apparatus allows Legionella pneumophila to establish a niche called the Legionella-containing vacuole (LCV), which is permissive for intracellular bacterial propagation. Among these proteins, substrate of Icm/Dot transporter (SidC) anchors to the cytoplasmic surface of the LCV and is important for the recruitment of host endoplasmic reticulum (ER) proteins to this organelle. However, the biochemical function underlying this activity is unknown. Here, we determined the structure of the N-terminal domain of SidC, which has no structural homology to any protein.Sequence homology analysis revealed a potential canonical catalytic triad formed by Cys46, His444, and Asp446 on the surface of SidC. Unexpectedly, we found that SidC is an E3 ubiquitin ligase that uses the C-H-D triad to catalyze the formation of highmolecular-weight polyubiquitin chains through multiple ubiquitin lysine residues. A C46A mutation completely abolished the E3 ligase activity and the ability of the protein to recruit host ER proteins as well as polyubiquitin conjugates to the LCV. Thus, SidC represents a unique E3 ubiquitin ligase family important for phagosomal membrane remodeling by L. pneumophila.