Browsing by Subject "Bacterial proteins"

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    Interactions between the Coxiella burnetii parasitophorous vacuole and the endoplasmic reticulum involve the host protein ORP1L
    (Wiley, 2017-01) Justis, Anna V.; Hansen, Bryan; Beare, Paul A.; King, Kourtney B.; Heinzen, Robert A.; Gilk, Stacey D.; Microbiology and Immunology, School of Medicine
    Coxiella burnetii is a gram-negative intracellular bacterium that forms a large, lysosome-like parasitophorous vacuole (PV) essential for bacterial replication. Host membrane lipids are critical for the formation and maintenance of this intracellular niche, yet the mechanisms by which Coxiella manipulates host cell lipid metabolism, trafficking and signalling are unknown. Oxysterol-binding protein-related protein 1 long (ORP1L) is a mammalian lipid-binding protein that plays a dual role in cholesterol-dependent endocytic trafficking as well as interactions between endosomes and the endoplasmic reticulum (ER). We found that ORP1L localized to the Coxiella PV within 12 h of infection through a process requiring the Coxiella Dot/Icm Type 4B secretion system, which secretes effector proteins into the host cell cytoplasm where they manipulate trafficking and signalling pathways. The ORP1L N-terminal ankyrin repeats were necessary and sufficient for PV localization, indicating that ORP1L binds a PV membrane protein. Strikingly, ORP1L simultaneously co-localized with the PV and ER, and electron microscopy revealed membrane contact sites between the PV and ER membranes. In ORP1L-depleted cells, PVs were significantly smaller than PVs from control cells. These data suggest that ORP1L is specifically recruited by the bacteria to the Coxiella PV, where it influences PV membrane dynamics and interactions with the ER.
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    Substrate Binding Mode and Molecular Basis of a Specificity Switch in Oxalate Decarboxylase
    (American Chemical Society, 2016-04-12) Zhu, Wen; Easthon, Lindsey M.; Reinhardt, Laurie A.; Tu, Chingkuang; Cohen, Steven E.; Silverman, David N.; Allen, Karen N.; Richards, Nigel G.J.; Department of Chemistry & Chemical Biology, School of Science
    Oxalate decarboxylase (OxDC) catalyzes the conversion of oxalate into formate and carbon dioxide in a remarkable reaction that requires manganese and dioxygen. Previous studies have shown that replacing an active-site loop segment Ser(161)-Glu(162)-Asn(163)-Ser(164) in the N-terminal domain of OxDC with the cognate residues Asp(161)-Ala(162)-Ser-(163)-Asn(164) of an evolutionarily related, Mn-dependent oxalate oxidase gives a chimeric variant (DASN) that exhibits significantly increased oxidase activity. The mechanistic basis for this change in activity has now been investigated using membrane inlet mass spectrometry (MIMS) and isotope effect (IE) measurements. Quantitative analysis of the reaction stoichiometry as a function of oxalate concentration, as determined by MIMS, suggests that the increased oxidase activity of the DASN OxDC variant is associated with only a small fraction of the enzyme molecules in solution. In addition, IE measurements show that C-C bond cleavage in the DASN OxDC variant proceeds via the same mechanism as in the wild-type enzyme, even though the Glu(162) side chain is absent. Thus, replacement of the loop residues does not modulate the chemistry of the enzyme-bound Mn(II) ion. Taken together, these results raise the possibility that the observed oxidase activity of the DASN OxDC variant arises from an increased level of access of the solvent to the active site during catalysis, implying that the functional role of Glu(162) is to control loop conformation. A 2.6 Å resolution X-ray crystal structure of a complex between oxalate and the Co(II)-substituted ΔE162 OxDC variant, in which Glu(162) has been deleted from the active site loop, reveals the likely mode by which the substrate coordinates the catalytically active Mn ion prior to C-C bond cleavage. The "end-on" conformation of oxalate observed in the structure is consistent with the previously published V/K IE data and provides an empty coordination site for the dioxygen ligand that is thought to mediate the formation of Mn(III) for catalysis upon substrate binding.