26 research outputs found
Selective Pressure for Biofilm Formation in Bacillus subtilis: Differential Effect of Mutations in the Master Regulator SinR on Bistability
Kampf J, Gerwig J, Kruse K, et al. Selective Pressure for Biofilm Formation in Bacillus subtilis: Differential Effect of Mutations in the Master Regulator SinR on Bistability. mBio. 2018;9(5): e01464-18
A widespread family of bacterial cell wall assembly proteins
Teichoic acids and acidic capsular polysaccharides are major anionic cell wall polymers (APs) in many bacteria, with various critical cell functions, including maintenance of cell shape and structural integrity, charge and cation homeostasis, and multiple aspects of pathogenesis. We have identified the widespread LytRâCps2AâPsr (LCP) protein family, of previously unknown function, as novel enzymes required for AP synthesis. Structural and biochemical analysis of several LCP proteins suggest that they carry out the final step of transferring APs from their lipid-linked precursor to cell wall peptidoglycan (PG). In Bacillus subtilis, LCP proteins are found in association with the MreB cytoskeleton, suggesting that MreB proteins coordinate the insertion of the major polymers, PG and AP, into the cell wall
Reaction mechanism for the replacement of calcite by dolomite and siderite: Implications for geochemistry, microstructure and porosity evolution during hydrothermal mineralisation
Carbonate reactions are common in mineral deposits due to CO2-rich mineralising fluids. This study presents the first in-depth, integrated analysis of microstructure and microchemistry of fluid-mediated carbonate reaction textures at hydrothermal conditions. In doing so, we describe the mechanisms by which carbonate phases replace one another, and the implications for the evolution of geochemistry, rock microstructures and porosity. The sample from the 1.95 Moz Junction gold deposit, Western Australia, contains calcite derived from carbonation of a metamorphic amphiboleâplagioclase assemblage that has further altered to siderite and dolomite. The calcite is porous and contains iron-rich calcite blebs interpreted to have resulted from fluid-mediated replacement of compositionally heterogeneous amphiboles. The siderite is polycrystalline but nucleates topotactically on the calcite. As a result, the boundaries between adjacent grains are low-angle boundaries (<10°), which are geometrically similar to those formed by crystalâplastic deformation and recovery. Growth zoning within individual siderite grains shows that the low-angle boundaries are growth features and not due to deformation. Low-angle boundaries develop due to the propagation of defects at grain faces and zone boundaries and by impingement of grains that nucleated with small misorientations relative to each other during grain growth.The cores of siderite grains are aligned with the twin planes in the parent calcite crystal showing that the reactant Fe entered the crystal along the twin boundaries. Dolomite grains, many of which appear to in-fill space generated by the siderite replacement, also show alignment of cores along the calcite twin planes, suggesting that they did not grow into space but replaced the calcite. Where dolomite is seen directly replacing calcite, it nucleates on the Fe-rich calcite due to the increased compatibility of the Fe-bearing calcite lattice relative to the pure calcite. Both reactions are interpreted as fluid-mediated replacement reactions which use the crystallography and elemental chemistry of the calcite. Experiments of fluid-mediated replacement reactions show that they proceed much faster than diffusion-based reactions. This is important when considering the rates of reactions relative to fluid flow in mineralising systems
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The interaction of signal sequences with the signal recognition particle
The signal recognition particle (SRP) is an RNA-protein complex that directs proteins containing an N-terminal signal sequence into the secretory pathway. For high fidelity in the selection of substrates for secretion, the SRP must recognize the features of signal sequences that uniquely distinguish them from other segments of proteins. The recognition of signal sequences by SRP is therefore almost certain to involve novel modes of protein-peptide interaction. Based on crosslinking data and the crystal structure of the SRP protein subunit Ffh, it is widely assumed, though unsubstantiated by experimental data, that the signal sequence binds to a hydrophobic groove on the âM-domainâ of Ffh. However, in this thesis data are presented from crosslinking experiments and from direct binding assays that strongly suggest the adjacent âNG-domainâ of Ffh contributes a substantial portion of the binding site for signal sequences. Using a zero-length crosslinking method previously untested in the SRP system, the binding site has been localized to the âG-domainâ, a subdomain within the NG domain that has a tertiary fold which is to a large extent typical of ras-like GTPases. Given that previous crosslinking studies have suggested the M-domain is at least in close proximity to the signal peptide, it is likely the signal peptide binds close to the interface between the two domains. Defining how the two domains interact is therefore essential for understanding how the SRP recognizes signal sequences. How the domains interact was left uncertain by the extensive packing interactions between molecules in the crystal structure of Ffh. The work in this thesis has defined a segment of the M-domain, termed the âfinger loopâ, which interacts with the NG domain. Finally, this thesis work has also explored the functional role of the RNA in the SRP. Data are presented leading to a model whereby the RNA stabilizes conformational states of Ffh in which the two domains are more loosely associated with each other. This may explain previous studies reports that RNA stimulates the association of Ffh with its receptor FtsY
EzrA: a spectrin-like scaffold in the bacterial cell division machinery
Much progress has been made in identifying the components of the divisome, the assembly of proteins that undertakes the vital process of cell division in bacteria. However, how the highly interdependent processes on either side of the membrane are coordinated during division is a major unresolved question. How is the degradation and synthesis of the cell wall on the outside of the cell coordinated with cytokinesis and membrane fission, which are driven from the inside of the cell by the tubulin homologue FtsZ? A possible key mediator of such coordination is the membrane protein EzrA, as it interacts both with FtsZ and the penicillin binding proteins (PBPs) that synthesize peptidoglycan. Cleverley et al. [Nature Communications (2014) 5, 5421] have recently solved the crystal structure of the cytoplasmic domain of B. subtilis EzrA, which points to an important scaffolding role for EzrA in the divisome. The structure resembles the eukaryotic, cytoskeletal spectrin proteins, which link actin filaments in the cytoskeleton and also connect the actin cytoskeleton to membrane-bound integrin proteins
Characterization of a CorA Mg2+ transport channel from Methanococcus jannaschii using a Thermofluor-based stability assay
Gold precipitation: the Big Picture from micro-chemical processes
Samples of gold-bearing laminated veins from the Sunrise Dam Gold Mine (Western Australia) have been investigated in detail using a combination of advanced imaging and analysis techniques (electron optics, proton-induced x-ray emission, laser ablation). This analysis reveals a very complex chemical and mechanical history recorded at the micro-scale which illustrates the complexity of simple vein systems and the nature of gold precipitation. The laminations represent
micro-breccias within a pre-existing quartz-carbonate vein. The gold is hosted by coarse pyrite but is intimately
associated with the precipitation of apatite, dolomite,
tourmaline-muscovite, rutile and zircon. The chemistry of
the apatite, in-situ Sr isotope analysis, the mineralogy of
the breccia and the coarse pyrite gold-host indicates that
two fluids were present in the system. An oxidised, CO2-
rich (water-poor), S-poor fluid with a strong mantle affinity and a water-bearing, reduced S, As, Fe-bearing fluid. The mixing of these two fluids during the cracking of a strong pre-existing quartz vein in a weak sheared host
rock led to gold localisation and precipitation
The Cryo-EM Structure of the CorA channel from Methanocaldococcus jannaschii in low magnesium conditions.
AbstractCorA channels are responsible for the uptake of essential magnesium ions by bacteria. X-ray crystal structures have been resolved for two full-length CorA channels, each in a non-conducting state with magnesium ions bound to the protein: These structures reveal a homo-pentameric quaternary structure with approximate 5-fold rotational symmetry about a central pore axis. We report the structure of the detergent solubilized Methanocaldococcus jannaschii CorA channel determined by Cryo-Electron Microscopy and Single Particle Averaging, supported by Small Angle X-ray Scattering and X-ray crystallography. This structure also shows a pentameric channel but with a highly asymmetric domain structure. The asymmetry of the domains includes differential separations between the trans-membrane segments, which reflects mechanical coupling of the cytoplasmic domain to the trans-membrane domain. This structure therefore reveals an important aspect of the gating mechanism of CorA channels by providing an indication of how the absence of magnesium ions leads to major structural changes
Gold precipitation: the Big Picture from micro-chemical\ud processes
Samples of gold-bearing laminated veins from the Sunrise Dam Gold Mine (Western Australia) have been investigated in detail using a combination of advanced imaging and analysis techniques (electron optics, proton-induced x-ray emission, laser ablation). This analysis reveals a very complex chemical and mechanical history recorded at the micro-scale which illustrates the complexity of simple vein systems and the nature of gold precipitation. The laminations represent\ud
micro-breccias within a pre-existing quartz-carbonate vein. The gold is hosted by coarse pyrite but is intimately\ud
associated with the precipitation of apatite, dolomite,\ud
tourmaline-muscovite, rutile and zircon. The chemistry of\ud
the apatite, in-situ Sr isotope analysis, the mineralogy of\ud
the breccia and the coarse pyrite gold-host indicates that\ud
two fluids were present in the system. An oxidised, CO2-\ud
rich (water-poor), S-poor fluid with a strong mantle affinity and a water-bearing, reduced S, As, Fe-bearing fluid. The mixing of these two fluids during the cracking of a strong pre-existing quartz vein in a weak sheared host\ud
rock led to gold localisation and precipitation
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The Structure of Escherichia coli Signal Recognition Particle Revealed by Scanning Transmission Electron Microscopy
Structural studies on various domains of the ribonucleoprotein signal recognition particle (SRP) have not converged on a single complete structure of bacterial SRP consistent with the biochemistry of the particle. We obtained a three-dimensional structure for Escherichia coli SRP by cryoscanning transmission electron microscopy and mapped the internal RNA by electron spectroscopic imaging. Crystallographic data were fit into the SRP reconstruction, and although the resulting model differed from previous models, they could be rationalized by movement through an interdomain linker of Ffh, the protein component of SRP. Fluorescence resonance energy transfer experiments determined interdomain distances that were consistent with our model of SRP. Docking our model onto the bacterial ribosome suggests a mechanism for signal recognition involving interdomain movement of Ffh into and out of the nascent chain exit site and suggests how SRP could interact and/or compete with the ribosome-bound chaperone, trigger factor, for a nascent chain during translation