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Microbiology (Reading, England) Oct 2023Multidrug efflux pumps are molecular machines that sit in the bacterial cell membrane and pump molecules out from either the periplasm or cytoplasm to outside the cell....
Multidrug efflux pumps are molecular machines that sit in the bacterial cell membrane and pump molecules out from either the periplasm or cytoplasm to outside the cell. While involved in a variety of biological roles, they are primarily known for their contribution to antibiotic resistance by limiting the intracellular accumulation of antimicrobial compounds within bacteria. These transporters are often overexpressed in clinical isolates, leading to multidrug-resistant phenotypes. Efflux pumps are classified into several families based on their structure and understanding the characteristics of each family is important for the development of novel therapies to restore antibiotic potency.
Topics: Humans; Cytoplasm; Periplasm; Cell Membrane; Anti-Bacterial Agents; Membrane Transport Proteins
PubMed: 37787650
DOI: 10.1099/mic.0.001370 -
Proceedings of the National Academy of... Aug 2023Trehalose plays a crucial role in the survival and virulence of the deadly human pathogen (). The type I ATP-binding cassette (ABC) transporter LpqY-SugABC is the sole...
Trehalose plays a crucial role in the survival and virulence of the deadly human pathogen (). The type I ATP-binding cassette (ABC) transporter LpqY-SugABC is the sole pathway for trehalose to enter . The substrate-binding protein, LpqY, which forms a stable complex with the translocator SugABC, recognizes and captures trehalose and its analogues in the periplasmic space, but the precise molecular mechanism for this process is still not well understood. This study reports a 3.02-Å cryoelectron microscopy structure of trehalose-bound LpqY-SugABC in the pretranslocation state, a crystal structure of LpqY in a closed form with trehalose bound and five crystal structures of LpqY in complex with different trehalose analogues. These structures, accompanied by substrate-stimulated ATPase activity data, reveal how LpqY recognizes and binds trehalose and its analogues, and highlight the flexibility in the substrate binding pocket of LpqY. These data provide critical insights into the design of trehalose analogues that could serve as potential molecular probe tools or as anti-TB drugs.
Topics: Humans; Cryoelectron Microscopy; Mycobacterium tuberculosis; Trehalose; ATP-Binding Cassette Transporters; Molecular Probes
PubMed: 37603751
DOI: 10.1073/pnas.2307625120 -
MBio Feb 2024Many temperate phages encode prophage-expressed functions that interfere with superinfection of the host bacterium by external phages. phage P22 has four such systems...
Many temperate phages encode prophage-expressed functions that interfere with superinfection of the host bacterium by external phages. phage P22 has four such systems that are expressed from the prophage in a lysogen that are encoded by the (repressor), , , and genes. Here we report that the P22-encoded SieA protein is necessary and sufficient for exclusion by the SieA system and that it is an inner membrane protein that blocks DNA injection by P22 and its relatives, but has no effect on infection by other tailed phage types. The P22 virion injects its DNA through the host cell membranes and periplasm via a conduit assembled from three "ejection proteins" after their release from the virion. Phage P22 mutants that overcome the SieA block were isolated, and they have amino acid changes in the C-terminal regions of the gene and encoded ejection proteins. Three different single-amino acid changes in these proteins are required to obtain nearly full resistance to SieA. Hybrid P22 phages that have phage HK620 ejection protein genes are also partially resistant to SieA. There are three sequence types of extant phage-encoded SieA proteins that are less than 30% identical to one another, yet comparison of two of these types found no differences in phage target specificity. Our data strongly suggest a model in which the inner membrane protein SieA interferes with the assembly or function of the periplasmic gp20 and membrane-bound gp16 DNA delivery conduit.IMPORTANCEThe ongoing evolutionary battle between bacteria and the viruses that infect them is a critical feature of bacterial ecology on Earth. Viruses can kill bacteria by infecting them. However, when their chromosomes are integrated into a bacterial genome as a prophage, viruses can also protect the host bacterium by expressing genes whose products defend against infection by other viruses. This defense property is called "superinfection exclusion." A significant fraction of bacteria harbor prophages that encode such protective systems, and there are many different molecular strategies by which superinfection exclusion is mediated. This report is the first to describe the mechanism by which bacteriophage P22 SieA superinfection exclusion protein protects its host bacterium from infection by other P22-like phages. The P22 prophage-encoded inner membrane SieA protein prevents infection by blocking transport of superinfecting phage DNA across the inner membrane during injection.
Topics: Humans; Bacteriophage P22; Superinfection; Bacteriophages; Prophages; Membrane Proteins; DNA; Amino Acids
PubMed: 38236051
DOI: 10.1128/mbio.02169-23 -
Proceedings of the National Academy of... Jul 2023The outer membrane of Gram-negative bacteria is unique in both structure and function. The surface-exposed outer leaflet is composed of lipopolysaccharide, while the...
The outer membrane of Gram-negative bacteria is unique in both structure and function. The surface-exposed outer leaflet is composed of lipopolysaccharide, while the inner leaflet is composed of glycerophospholipids. This lipid asymmetry creates mechanical strength, lowers membrane permeability, and is necessary for virulence in many pathogens. Glycerophospholipids that mislocalize to the outer leaflet are removed by the Mla pathway, which consists of the outer membrane channel MlaA, the periplasmic lipid carrier MlaC, and the inner membrane transporter MlaBDEF. The opportunistic pathogen has two proteins of the MlaA family: PA2800 and PA3239. Here, we show that PA2800 is part of a canonical Mla pathway, while PA3239 functions with the putative lipase PA3238. While loss of either pathway individually has little to no effect on outer membrane integrity, loss of both pathways weakens the outer membrane permeability barrier and increases production of the secondary metabolite pyocyanin. We propose that mislocalized glycerophospholipids are removed from the outer leaflet by PA3239 (renamed MlaZ), transferred to PA3238 (renamed MlaY), and degraded. This pathway streamlines recycling of glycerophospholipid degradation products by removing glycerophospholipids from the outer leaflet prior to degradation.
Topics: Membrane Lipids; Pseudomonas aeruginosa; Biological Transport; Phospholipases; Bacterial Outer Membrane Proteins; Cell Membrane; Glycerophospholipids
PubMed: 37463202
DOI: 10.1073/pnas.2302546120 -
Nature Communications Dec 2023The outer membrane (OM) of Gram-negative bacteria is an asymmetric lipid bilayer with outer leaflet lipopolysaccharides and inner leaflet phospholipids (PLs). This...
The outer membrane (OM) of Gram-negative bacteria is an asymmetric lipid bilayer with outer leaflet lipopolysaccharides and inner leaflet phospholipids (PLs). This unique lipid asymmetry renders the OM impermeable to external insults, including antibiotics and bile salts. To maintain this barrier, the OmpC-Mla system removes mislocalized PLs from the OM outer leaflet, and transports them to the inner membrane (IM); in the first step, the OmpC-MlaA complex transfers PLs to the periplasmic chaperone MlaC, but mechanistic details are lacking. Here, we biochemically and structurally characterize the MlaA-MlaC transient complex. We map the interaction surfaces between MlaA and MlaC in Escherichia coli, and show that electrostatic interactions are important for MlaC recruitment to the OM. We further demonstrate that interactions with MlaC modulate conformational states in MlaA. Finally, we solve a 2.9-Å cryo-EM structure of a disulfide-trapped OmpC-MlaA-MlaC complex in nanodiscs, reinforcing the mechanism of MlaC recruitment, and highlighting membrane thinning as a plausible strategy for directing lipids for transport. Our work offers critical insights into retrograde PL transport by the OmpC-Mla system in maintaining OM lipid asymmetry.
Topics: Bacterial Outer Membrane; Biological Transport; Membrane Lipids; Lipid Bilayers; Escherichia coli; Phospholipids; Escherichia coli Proteins; Bacterial Outer Membrane Proteins; Lipopolysaccharides; Cell Membrane
PubMed: 38092770
DOI: 10.1038/s41467-023-44144-8 -
Nature Communications Oct 2023Mycobacterium tuberculosis is protected from antibiotic therapy by a multi-layered hydrophobic cell envelope. Major facilitator superfamily (MFS) transporter Rv1410 and...
Mycobacterium tuberculosis is protected from antibiotic therapy by a multi-layered hydrophobic cell envelope. Major facilitator superfamily (MFS) transporter Rv1410 and the periplasmic lipoprotein LprG are involved in transport of triacylglycerides (TAGs) that seal the mycomembrane. Here, we report a 2.7 Å structure of a mycobacterial Rv1410 homologue, which adopts an outward-facing conformation and exhibits unusual transmembrane helix 11 and 12 extensions that protrude ~20 Å into the periplasm. A small, very hydrophobic cavity suitable for lipid transport is constricted by a functionally important ion-lock likely involved in proton coupling. Combining mutational analyses and MD simulations, we propose that TAGs are extracted from the core of the inner membrane into the central cavity via lateral clefts present in the inward-facing conformation. The functional role of the periplasmic helix extensions is to channel the extracted TAG into the lipid binding pocket of LprG.
Topics: Membrane Transport Proteins; Mycobacterium tuberculosis; Biological Transport; Membranes; Lipids; Protein Conformation
PubMed: 37833269
DOI: 10.1038/s41467-023-42073-0 -
The Journal of Biological Chemistry Sep 2023Maintaining a functional proteome under different environmental conditions is challenging for every organism, in particular for unicellular organisms, such as bacteria.... (Review)
Review
Maintaining a functional proteome under different environmental conditions is challenging for every organism, in particular for unicellular organisms, such as bacteria. In order to cope with changing environments and stress conditions, bacteria depend on strictly coordinated proteostasis networks that control protein production, folding, trafficking, and degradation. Regulation of ribosome biogenesis and protein synthesis are cornerstones of this cellular adaptation in all domains of life, which is rationalized by the high energy demand of both processes and the increased resistance of translationally silent cells against internal or external poisons. Reduced protein synthesis ultimately also reduces the substrate load for protein transport systems, which are required for maintaining the periplasmic, inner, and outer membrane subproteomes. Consequences of impaired protein transport have been analyzed in several studies and generally induce a multifaceted response that includes the upregulation of chaperones and proteases and the simultaneous downregulation of protein synthesis. In contrast, generally less is known on how bacteria adjust the protein targeting and transport machineries to reduced protein synthesis, e.g., when cells encounter stress conditions or face nutrient deprivation. In the current review, which is mainly focused on studies using Escherichia coli as a model organism, we summarize basic concepts on how ribosome biogenesis and activity are regulated under stress conditions. In addition, we highlight some recent developments on how stress conditions directly impair protein targeting to the bacterial membrane. Finally, we describe mechanisms that allow bacteria to maintain the transport of stress-responsive proteins under conditions when the canonical protein targeting pathways are impaired.
Topics: Adaptation, Psychological; Escherichia coli; Escherichia coli Proteins; Heat-Shock Proteins; Protein Biosynthesis; Protein Transport
PubMed: 37586589
DOI: 10.1016/j.jbc.2023.105163 -
Bio Systems Sep 2023Copper is essential for life, but is toxic in excess. Copper homeostasis is achieved in the cytoplasm and the periplasm as a unique feature of Gram-negative bacteria....
Copper is essential for life, but is toxic in excess. Copper homeostasis is achieved in the cytoplasm and the periplasm as a unique feature of Gram-negative bacteria. Especially, it has become clear the role of the periplasm and periplasmic proteins regarding whole-cell copper homeostasis. Here, we addressed the role of the periplasm and periplasmic proteins in copper homeostasis using a Systems Biology approach integrating experiments with models. Our analysis shows that most of the copper-bound molecules localize in the periplasm but not cytoplasm, suggesting that Escherichia coli utilizes the periplasm to sense the copper concentration in the medium and sequester copper ions. In particular, a periplasmic multi-copper oxidase CueO and copper-responsive transcriptional factor CusS contribute both to protection against Cu(I) toxicity and to incorporating copper into the periplasmic components/proteins. We propose that Gram-negative bacteria have evolved mechanisms to sense and store copper in the periplasm to expand their living niches.
Topics: Escherichia coli Proteins; Periplasm; Periplasmic Proteins; Escherichia coli; Homeostasis
PubMed: 37453610
DOI: 10.1016/j.biosystems.2023.104980 -
Microbiology and Molecular Biology... Jun 2024SUMMARYInfectious bacteria have both intrinsic and acquired mechanisms to combat harmful biocides that enter the cell. Through adaptive pressures, many of these... (Review)
Review
SUMMARYInfectious bacteria have both intrinsic and acquired mechanisms to combat harmful biocides that enter the cell. Through adaptive pressures, many of these pathogens have become resistant to many, if not all, of the current antibiotics used today to treat these often deadly infections. One prominent mechanism is the upregulation of efflux systems, especially the resistance-nodulation-cell division class of exporters. These tripartite systems consist of an inner membrane transporter coupled with a periplasmic adaptor protein and an outer membrane channel to efficiently transport a diverse array of substrates from inside the cell to the extracellular space. Detailed mechanistic insight into how these inner membrane transporters recognize and shuttle their substrates can ultimately inform both new antibiotic and efflux pump inhibitor design. This review examines the structural basis of substrate recognition of these pumps and the molecular mechanisms underlying multidrug extrusion, which in turn mediate antimicrobial resistance in bacterial pathogens.
Topics: Membrane Transport Proteins; Anti-Bacterial Agents; Bacteria; Bacterial Proteins; Cell Division; Drug Resistance, Multiple, Bacterial; Biological Transport; Models, Molecular; Drug Resistance, Bacterial
PubMed: 38551344
DOI: 10.1128/mmbr.00198-23 -
Nature Microbiology Jul 2023Bdellovibrio bacteriovorus is a microbial predator that offers promise as a living antibiotic for its ability to kill Gram-negative bacteria, including human pathogens....
Bdellovibrio bacteriovorus is a microbial predator that offers promise as a living antibiotic for its ability to kill Gram-negative bacteria, including human pathogens. Even after six decades of study, fundamental details of its predation cycle remain mysterious. Here we used cryo-electron tomography to comprehensively image the lifecycle of B. bacteriovorus at nanometre-scale resolution. With high-resolution images of predation in a native (hydrated, unstained) state, we discover several surprising features of the process, including macromolecular complexes involved in prey attachment/invasion and a flexible portal structure lining a hole in the prey peptidoglycan that tightly seals the prey outer membrane around the predator during entry. Unexpectedly, we find that B. bacteriovorus does not shed its flagellum during invasion, but rather resorbs it into its periplasm for degradation. Finally, following growth and division in the bdelloplast, we observe a transient and extensive ribosomal lattice on the condensed B. bacteriovorus nucleoid.
Topics: Humans; Animals; Bdellovibrio; Electron Microscope Tomography; Predatory Behavior; Bdellovibrio bacteriovorus
PubMed: 37349588
DOI: 10.1038/s41564-023-01401-2