2751
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Viveiros M, Jesus A, Brito M, Leandro C, Martins M, Ordway D, Molnar AM, Molnar J, Amaral L. Inducement and reversal of tetracycline resistance in Escherichia coli K-12 and expression of proton gradient-dependent multidrug efflux pump genes. Antimicrob Agents Chemother 2005; 49:3578-82. [PMID: 16048990 PMCID: PMC1196278 DOI: 10.1128/aac.49.8.3578-3582.2005] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Expression of eight transporter genes of Escherichia coli K-12 and its DeltaacrAB mutant prior to and after induction of both strains to tetracycline resistance and after reversal of induced resistance were analyzed by quantitative reverse transcriptase PCR. All transporter genes were overexpressed after induced resistance with acrF being 80-fold more expressed in the DeltaacrAB tetracycline-induced strain.
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Affiliation(s)
- Miguel Viveiros
- Unit of Mycobacteriology, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Rua Junqueira 96, 1349-008 Lisbon, Portugal
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2752
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Abstract
Several bacteria that are pathogenic to animals also infect plants. Mechanistic studies have proven that some human/animal pathogenic bacteria employ a similar subset of virulence determinants to elicit disease in animals, invertebrates and plants. Therefore, the results of plant infection studies are relevant to animal pathogenesis. This discovery has resulted in the development of convenient, cost-effective, and reliable plant infection models to study the molecular basis of infection by animal pathogens. Plant infection models provide a number of advantages in the study of animal pathogenesis. Using a plant model, mutations in animal pathogenic bacteria can easily be screened for putative virulence factors, a process which if done using existing animal infection models would be time-consuming and tedious. High-throughput screening of plants also provides the potential for unravelling the mechanisms by which plants resist animal pathogenic bacteria, and provides a means to discover novel therapeutic agents such as antibiotics and anti-infective compounds. In this review, we describe the developing technique of using plants as a model system to study Pseudomonas aeruginosa, Enterococcus faecalis and Staphylococcus aureus pathogenesis, and discuss ways to use this new technology against disease warfare and other types of bioterrorism.
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Affiliation(s)
- B Prithiviraj
- Department of Horticulture and Landscape Architecture, Colorado State University, Fort Collins, CO 80523-1173, USA
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2753
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Woebking B, Reuter G, Shilling RA, Velamakanni S, Shahi S, Venter H, Balakrishnan L, van Veen HW. Drug-lipid A interactions on the Escherichia coli ABC transporter MsbA. J Bacteriol 2005; 187:6363-9. [PMID: 16159769 PMCID: PMC1236644 DOI: 10.1128/jb.187.18.6363-6369.2005] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2005] [Accepted: 06/22/2005] [Indexed: 11/20/2022] Open
Abstract
MsbA is an essential ATP-binding cassette half-transporter in the cytoplasmic membrane of the gram-negative Escherichia coli and is required for the export of lipopolysaccharides (LPS) to the outer membrane, most likely by transporting the lipid A core moiety. Consistent with the homology of MsbA to the multidrug transporter LmrA in the gram-positive Lactococcus lactis, our recent work in E. coli suggested that MsbA might interact with multiple drugs. To enable a more detailed analysis of multidrug transport by MsbA in an environment deficient in LPS, we functionally expressed MsbA in L. lactis. MsbA expression conferred an 86-fold increase in resistance to the macrolide erythromycin. A kinetic characterization of MsbA-mediated ethidium and Hoechst 33342 transport revealed apparent single-site kinetics and competitive inhibition of these transport reactions by vinblastine with K(i) values of 16 and 11 microM, respectively. We also detected a simple noncompetitive inhibition of Hoechst 33342 transport by free lipid A with a K(i) of 57 microM, in a similar range as the K(i) for vinblastine, underscoring the relevance of our LPS-less lactococcal model for studies on MsbA-mediated drug transport. These observations demonstrate the ability of heterologously expressed MsbA to interact with free lipid A and multiple drugs in the absence of auxiliary E. coli proteins. Our transport data provide further functional support for direct LPS-MsbA interactions as observed in a recent crystal structure for MsbA from Salmonella enterica serovar Typhimurium (C. L. Reyes and G. Chang, Science 308:1028-1031, 2005).
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Affiliation(s)
- Barbara Woebking
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
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2754
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Walker SL, Redman JA, Elimelech M. Influence of growth phase on bacterial deposition: interaction mechanisms in packed-bed column and radial stagnation point flow systems. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2005; 39:6405-11. [PMID: 16190193 DOI: 10.1021/es050077t] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The influence of bacterial growth stage on cell deposition kinetics has been examined using a mutant of Escherichia coli K12. Two experimental techniques--a packed-bed column and a radial stagnation point flow (RSPF) system--were employed to determine bacterial deposition rates onto quartz surfaces over a wide range of solution ionic strengths. Stationary-phase cells were found to be more adhesive than mid-exponential phase cells in both experimental systems. The divergence in deposition behavior was notably more pronounced in the RSPF than in the packed-bed system. For instance, in the RSPF system, the deposition rate of the stationary-phase cells at 0.03 M ionic strength was 14 times greater than that of the mid-exponential cells. The divergence in the packed-bed system was most significant at 0.01 M, where the deposition rate for the stationary-phase cells was nearly 4 times greater than for the mid-exponential cells. To explain the observed adhesion behavior, the stationary and mid-exponential bacterial cells were characterized for their size, surface charge density, electrophoretic mobility, viability, and hydrophobicity. On the basis of this analysis, it is suggested that the stationary cells have a more heterogeneous distribution of charged functional groups on the bacterial surface than the mid-exponential cells, which results in higher deposition kinetics. Furthermore, because the RSPF system enumerates only bacterial cells retained in primary minima, whereas the packed column captures mostly cells deposited in secondary minima, the difference in the stationary and mid-exponential cell deposition kinetics is much more pronounced in the RSPF system.
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Affiliation(s)
- Sharon L Walker
- Department of Chemical and Environmental Engineering, University of California, Riverside, Riverside, California 92521, USA.
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2755
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Hiller M, Krabben L, Vinothkumar KR, Castellani F, van Rossum BJ, Kühlbrandt W, Oschkinat H. Solid-State Magic-Angle Spinning NMR of Outer-Membrane Protein G from Escherichia coli. Chembiochem 2005; 6:1679-84. [PMID: 16138308 DOI: 10.1002/cbic.200500132] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Uniformly 13C-,15N-labelled outer-membrane protein G (OmpG) from Escherichia coli was expressed for structural studies by solid-state magic-angle spinning (MAS) NMR. Inclusion bodies of the recombinant, labelled protein were purified under denaturing conditions and refolded in detergent. OmpG was reconstituted into lipid bilayers and several milligrams of two-dimensional crystals were obtained. Solid-state MAS NMR spectra showed signals with an apparent line width of 80-120 Hz (including homonuclear scalar couplings). Signal patterns for several amino acids, including threonines, prolines and serines were resolved and identified in 2D proton-driven spin-diffusion (PDSD) spectra.
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Affiliation(s)
- Matthias Hiller
- Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
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2756
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Abstract
Stress protection is an important but costly contributor to bacterial survival. Two distinct forms of environmental protection share a common cost and a significant species-wide variability. Porin-mediated outer membrane permeability and the RpoS-controlled general stress response both involve a trade-off between self-preservation and nutritional competence, called the SPANC balance. Interestingly, different Escherichia coli strains exhibit distinct settings of the SPANC balance. It is tilted towards high stress resistance and a restricted diet in some isolates whereas others have broader nutritional capability and better nutrient affinity but lower levels of resistance. Growth- or stress-related selective pressures working in opposite directions (antagonistic pleiotropy) result in polymorphisms affecting porins and RpoS. Consequently, these important cellular components are present at distinct concentrations in different isolates. A generalized hypothesis to explain bacterial adaptation, based on the SPANC investigations, is offered. A holistic approach to bacterial adaptation, involving a gamut of regulation and mutation, is likely to be the norm in broadening the capabilities of a species. Indeed, there is unlikely to be a standard regulatory setting typical for all members of a species. Gene regulation provides a limited fine control for maintaining the right level of adaptation in a particular niche but mutational changes provide the coarse control for adaptation between the species-wide environments of free-living bacteria.
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Affiliation(s)
- Thomas Ferenci
- School of Molecular and Microbial Biosciences, The University of Sydney, NSW 2006, Australia.
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2757
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Abstract
A method is proposed for the rapid classification of Gram-negative Enterobacteria using on-slide solubilization and trypsin digestion of proteins, followed by MALDI-TOF MS analysis. Peptides were identified from tryptic digests using microsequencing by tandem mass spectrometry and database searches. Proteins from the outer membrane family (OMP) were consistently identified in the Enterobacteria Escherichia coli, Enterobacter cloacae, Erwinia herbicola, and Salmonella typhimurium. Database searches indicate that these OMP peptides observed are unique to the Enterobacteria order.
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Affiliation(s)
- Patrick Pribil
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA
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2758
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Létoffé S, Wecker K, Delepierre M, Delepelaire P, Wandersman C. Activities of the Serratia marcescens heme receptor HasR and isolated plug and beta-barrel domains: the beta-barrel forms a heme-specific channel. J Bacteriol 2005; 187:4637-45. [PMID: 15968075 PMCID: PMC1151761 DOI: 10.1128/jb.187.13.4637-4645.2005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Serratia marcescens hemophore-specific outer membrane receptor HasR is a member of the TonB-dependent family of autoregulated receptors. It can transport either heme itself or heme bound to the hemophore HasA. On the basis of sequence and functional similarities with other TonB-dependent outer membrane receptors whose three-dimensional structures have been determined, a HasR structure model was proposed. The mature HasR protein comprises a 99-residue amino-terminal extension necessary for hasR transcription, followed by a plug domain of 139 amino acids and a beta-barrel domain inserted in the outer membrane, the lumen of which is closed by the plug. This model was used to generate hasR deletions encoding HasR proteins with the native signal peptides but lacking either the N-terminal regulatory extension or encoding the plug or the beta-barrel alone. The protein lacking the N-terminal extension, HasR delta11-91, was incorporated in the outer membrane and was fully functional for active uptake of free and hemophore-bound heme. The HasR beta-barrel, delta11-192, was also incorporated in the outer membrane and bound the hemophore but expressed no active heme transport properties. The HasR plug remained in the periplasm. Coexpression of the plug and the beta-barrel allowed partial plug insertion in the outer membrane, demonstrating that these two HasR domains interact in vivo. The beta-barrel and the plug also interact in vitro. Nevertheless, the two domains did not complement each other to reconstitute an active TonB-dependent receptor for free or hemophore-bound heme uptake. Production of the beta-barrel alone selectively increased passive diffusion of heme but not of other exogenous compounds. A mutation at histidine 603, which is required for heme uptake through the wild-type receptor, abolished heme diffusion, showing that HasR delta11-192 forms a specific heme channel.
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Affiliation(s)
- Sylvie Létoffé
- Unité des Membranes Bactériennes, Institut Pasteur, CNRS URA 2172, 25 rue du Dr Roux, 75724 Paris Cedex 15, France
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2759
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Ananta E, Voigt D, Zenker M, Heinz V, Knorr D. Cellular injuries upon exposure of Escherichia coli and Lactobacillus rhamnosus to high-intensity ultrasound. J Appl Microbiol 2005; 99:271-8. [PMID: 16033457 DOI: 10.1111/j.1365-2672.2005.02619.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
AIMS To examine cellular injuries occurring in cells of Escherichia coli (Gram-negative bacteria) and Lactobacillus rhamnosus (Gram-positive bacteria) in response to a high-intensity ultrasound treatment using classical plate count technique and flow cytometry. METHOD AND RESULTS According to plate count results, E. coli (D-value 8.3 min) was far more sensitive than L. rhamnosus (D-value 18.1 min) in their response to the ultrasound intensity applied (20 kHz, 17.6 W). The dye precursor carboxyfluorescein diacetate (cFDA) could freely diffuse across the cytoplasmic membrane of intact cells of Gram-positive bacteria L. rhamnosus, resulting in its intracellular enzymatic conversion and emission of green fluorescence. In contrast, the presence of an outer membrane on E. coli, which represents the class of Gram-negative bacteria, apparently disabled the penetration of viability marker cFDA. Ultrasound application on E. coli yielded in an increasing population with disintegrated outer membrane, which allowed penetration of cFDA and its intracellular enzymatic conversion as well as accumulation. In both organisms evaluated only a small population was labelled by propidium iodide upon exposure to ultrasound for up to 20 min. Within the experimental conditions investigated ultrasound did not considerably affect the cytoplasmic membrane, although according to plate count results viability loss occurred. CONCLUSIONS The results compiled suggest, that ultrasound induced cell death, which may not be related to membrane damage. SIGNIFICANCE AND IMPACT OF THE STUDY Limitation on the use of bacteriocins, which are aimed on destabilization of cytoplasmic membrane but inhibited by the outer membrane, could be overcome by ultrasound-assisted physical disruption of the outer membrane.
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Affiliation(s)
- E Ananta
- Department of Food Biotechnology and Food Process Engineering, Berlin University of Technology, Berlin, Germany
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2760
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Hünten P, Costa-Riu N, Palm D, Lottspeich F, Benz R. Identification and characterization of PorH, a new cell wall channel of Corynebacterium glutamicum. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1715:25-36. [PMID: 16112217 DOI: 10.1016/j.bbamem.2005.07.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2005] [Revised: 07/07/2005] [Accepted: 07/26/2005] [Indexed: 11/26/2022]
Abstract
The cell wall of Corynebacterium glutamicum contains the cation-selective channel (porin) PorA(C.glut) and the anion-selective channel PorB(C.glut) for the passage of hydrophilic solutes. Lipid bilayer experiments with organic solvent extracts of whole C. glutamicum cells cultivated in minimal medium suggested that also another cation-selective channel-forming protein, named PorH(C.glut), is present in C. glutamicum. The protein was purified to homogeneity by fast-protein liquid chromatography across a HiTrap-Q column. The pure protein had an apparent molecular mass of about 12 kDa on SDS-PAGE. Western blot analysis suggested that the cell wall channel is presumably formed by protein oligomers. The purified protein forms cation-selective channels with an average single-channel conductance of about 2.5 nS in 1 M KCl in the lipid bilayer assay. The PorH(C.glut) protein was partially sequenced, and based on the resulting amino acid sequence, the corresponding gene, designated as porH(C.glut), was identified in the published genome sequence of C. glutamicum ATCC13032. PorH(C.glut) contains only the inducer methionine but no N-terminal extension, which suggests that the export and assembly of the protein follow a yet unknown pathway. PorH(C.glut) is coded in the bacterial chromosome by a gene that is localized in the vicinity of porA(C.glut), within a putative operon of 13 genes. RT-PCR revealed that both porins are cotranscribed. They coexist according to immunological detection experiments in the cell wall of C. glutamicum together with PorB(C.glut) and PorC(C.glut).
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Affiliation(s)
- Peter Hünten
- Lehrstuhl für Biotechnologie, Biozentrum der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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2761
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Zorko M, Majerle A, Sarlah D, Keber MM, Mohar B, Jerala R. Combination of antimicrobial and endotoxin-neutralizing activities of novel oleoylamines. Antimicrob Agents Chemother 2005; 49:2307-13. [PMID: 15917526 PMCID: PMC1140490 DOI: 10.1128/aac.49.6.2307-2313.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A combination of antimicrobial and endotoxin-neutralizing activities is desired in order to prevent progression from infection to sepsis due to the release of lipopolysaccharide from dying gram-negative bacteria. Lipopolyamines have emerged as a new type of endotoxin-neutralizing compound, but their antimicrobial activity has not been investigated. We synthesized a series of 10 oleoylamines differing in the polyamino head group, particularly in the number and separation between nitrogen atoms and the position of the oleoyl moiety. Compounds showed activity against both gram-negative and gram-positive bacteria in the micromolar range. Compounds were able to provide penetration of ethidium bromide into bacteria, indicating effects on the bacterial membrane. Oleoylamines neutralized endotoxin in Limulus amoebocyte lysate assays and by neutralization of tumor necrosis factor alpha release in human blood. Comparison of biological activities of compounds identified structural properties responsible for antimicrobial activity, and quantitative structure-property relationship analysis provided a quantitative model for prediction of activity of oleoylamines.
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Affiliation(s)
- Mateja Zorko
- Laboratory of Biotechnology, National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia
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2762
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Hadjivassileva T, Thurston DE, Taylor PW. Pyrrolobenzodiazepine dimers: novel sequence-selective, DNA-interactive, cross-linking agents with activity against Gram-positive bacteria. J Antimicrob Chemother 2005; 56:513-8. [PMID: 16024592 DOI: 10.1093/jac/dki256] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
OBJECTIVES Pyrrolo[2,1-c][1,4]benzodiazepine (PBD) dimers are synthetic sequence-selective interstrand DNA minor-groove cross-linking agents developed from anthramycins. We investigated the antibacterial activity of three dimers, SJG-136, DRG-16 and ELB-21, which differ in the structure of the PBD monomeric unit and the length of the linker region between the two identical PBD monomers. METHODS MICs were determined against 38 methicillin-resistant Staphylococcus aureus (MRSA), 20 vancomycin-resistant enterococci (VRE), 12 isolates of Streptococcus pyogenes, 12 of Streptococcus agalactiae, 12 of Listeria monocytogenes and 24 Gram-negative clinical isolates. Binding to double-stranded DNA was assessed by determination of the DNA melting temperature (T(m)). RESULTS MIC(90) values for SJG-136 were 0.5 mg/L against MRSA, VRE and L. monocytogenes, 0.06 mg/L against S. pyogenes and 0.03 mg/L against S. agalactiae; these were below the maximum tolerated dose of the drug. MIC(90)s for DRG-16 were 0.125, >0.5, 0.125, 0.015 and <0.008 mg/L, respectively. The most potent compound was ELB-21, with corresponding MIC(90) values of 0.03, 0.06, 0.06, 0.015 and 0.015 mg/L. There was little or no variation in sensitivity amongst isolates from any one species. All Gram-negative species (Acinetobacter, Pseudomonas, Klebsiella, Proteus spp.) were not susceptible due to the barrier function of the outer membrane. PBD dimers showed bactericidal activity against MRSA and VRE and there was a significant post-antibiotic effect (1.5--3.5 h). Incubation of EMRSA-16 genomic DNA (50 microM) with 20 microM ELB-21 resulted in a large increase in T(m) suggesting that PBD dimers exert their antibacterial effect by cross-linking of the two DNA strands. CONCLUSIONS These data indicate that this novel class of antibacterial agents warrants further investigation as potential antibiotics for the treatment of severe infections caused by Gram-positive pathogens.
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2763
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Müller D, Benz I, Tapadar D, Buddenborg C, Greune L, Schmidt MA. Arrangement of the translocator of the autotransporter adhesin involved in diffuse adherence on the bacterial surface. Infect Immun 2005; 73:3851-9. [PMID: 15972470 PMCID: PMC1168569 DOI: 10.1128/iai.73.7.3851-3859.2005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Autotransporters of gram-negative bacteria are single-peptide secretion systems that consist of a functional N-terminal alpha-domain ("passenger") fused to a C-terminal beta-domain ("translocator"). How passenger proteins are translocated through the outer membrane has not been resolved, and at present essentially three different models are discussed. In the widely accepted "hairpin model" the passenger proteins are translocated through a channel formed by the beta-barrel of the translocator that is integrated in the outer membrane. This model has been challenged by a recent proposal for a general autotransporter model suggesting that there is a hexameric translocation pore that is generated by the oligomerization of six beta-domains. A third model suggests that conserved Omp85 participates in autotransporter integration and passenger protein translocation. To examine these models, in this study we investigated the presence of putative oligomeric structures of the translocator of the autotransporter adhesin involved in diffuse adherence (AIDA) in vivo by cross-linking techniques. Furthermore, the capacity of isolated AIDA fusion proteins to form oligomers was studied in vitro by several complementary analytical techniques, such as analytical gel filtration, electron microscopy, immunogold labeling, and cross-linking of recombinant autotransporter proteins in which different passenger proteins were fused to the AIDA translocator. Our results show that the AIDA translocator is mostly present as a monomer. Only a fraction of the AIDA autotransporter was found to form dimers on the bacterial surface and in solution. Higher-order structures, such as hexamers, were not detected either in vivo or in vitro and can therefore be excluded as functional moieties for the AIDA autotransporter.
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Affiliation(s)
- Daniel Müller
- Institut für Infektiologie, Zentrum für Molekularbiologie der Entzündung (ZMBE), Westfälische Wilhelms-Universität, Von-Esmarch-Str. 56, D-48149 Münster, Germany
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2764
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Fisseha M, Chen P, Brandt B, Kijek T, Moran E, Zollinger W. Characterization of native outer membrane vesicles from lpxL mutant strains of Neisseria meningitidis for use in parenteral vaccination. Infect Immun 2005; 73:4070-80. [PMID: 15972495 PMCID: PMC1168616 DOI: 10.1128/iai.73.7.4070-4080.2005] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Native outer membrane vesicles (NOMV) of Neisseria meningitidis consist of intact outer membrane and contain outer membrane proteins (OMP) and lipooligosaccharides (LOS) in their natural conformation and membrane environment. NOMV have been safely used intranasally in P1 studies with encouraging results, but they are too toxic for parenteral vaccination. We now report the preparation and characterization of lpxL mutants that express LOS with reduced toxicity, and the evaluation of the potential of NOMV from these strains for use as a parenteral vaccine. A series of deletion mutants were prepared with knockouts of one or more of the lpxL1, lpxL2, or synX genes. The deltalpxL2 mutants had a reduced growth rate, reduced level of LOS expression, and increased sensitivity to surfactants. In addition, deltasynX deltalpxL2 double mutants had reduced viability in stationary phase. The deltalpxL1 deltalpxL2 double mutant behaved essentially the same as the deltalpxL2 single mutant. LOS from both lpxL mutant strains exhibited altered migration on polyacrylamide gels. The LOS of deltalpxL2 mutants of L3,7 strains were fully sialylated. NOMV prepared from lpxL2 mutants was about 200-fold less active than wild-type NOMV in rabbit pyrogen tests and in tumor necrosis factor alpha release assays. Bactericidal titers induced in animals by deltalpxL2 mutant NOMV were lower than those induced by deltalpxL1 or wild-type NOMV. However, immunogenicity could be largely restored by use of an adjuvant. These results provide evidence that NOMV from deltalpxL2 mutant strains will be safe and immunogenic in humans when given parenterally.
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Affiliation(s)
- Makda Fisseha
- The Walter Reed Army Institute of Research, 503 Robert Grant Ave., Silver Spring, Maryland 20910-7500, USA
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2765
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Afkar E, Reguera G, Schiffer M, Lovley DR. A novel Geobacteraceae-specific outer membrane protein J (OmpJ) is essential for electron transport to Fe(III) and Mn(IV) oxides in Geobacter sulfurreducens. BMC Microbiol 2005; 5:41. [PMID: 16000176 PMCID: PMC1186022 DOI: 10.1186/1471-2180-5-41] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Accepted: 07/06/2005] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Metal reduction is thought to take place at or near the bacterial outer membrane and, thus, outer membrane proteins in the model dissimilatory metal-reducing organism Geobacter sulfurreducens are of interest to understand the mechanisms of Fe(III) reduction in the Geobacter species that are the predominant Fe(III) reducers in many environments. Previous studies have implicated periplasmic and outer membrane cytochromes in electron transfer to metals. Here we show that the most abundant outer membrane protein of G. sulfurreducens, OmpJ, is not a cytochrome yet it is required for metal respiration. RESULTS When outer membrane proteins of G. sulfurreducens were separated via SDS-PAGE, one protein, designated OmpJ (outer membrane protein J), was particularly abundant. The encoding gene, which was identified from mass spectrometry analysis of peptide fragments, is present in other Geobacteraceae, but not in organisms outside this family. The predicted localization and structure of the OmpJ protein suggested that it was a porin. Deletion of the ompJ gene in G. sulfurreducens produced a strain that grew as well as the wild-type strain with fumarate as the electron acceptor but could not grow with metals, such as soluble or insoluble Fe(III) and insoluble Mn(IV) oxide, as the electron acceptor. The heme c content in the mutant strain was ca. 50% of the wild-type and there was a widespread loss of multiple cytochromes from soluble and membrane fractions. Transmission electron microscopy analyses of mutant cells revealed an unusually enlarged periplasm, which is likely to trigger extracytoplasmic stress response mechanisms leading to the degradation of periplasmic and/or outer membrane proteins, such as cytochromes, required for metal reduction. Thus, the loss of the capacity for extracellular electron transport in the mutant could be due to the missing c-type cytochromes, or some more direct, but as yet unknown, role of OmpJ in metal reduction. CONCLUSION OmpJ is a putative porin found in the outer membrane of the model metal reducer G. sulfurreducens that is required for respiration of extracellular electron acceptors such as soluble and insoluble metals. The effect of OmpJ in extracellular electron transfer is indirect, as OmpJ is required to keep the integrity of the periplasmic space necessary for proper folding and functioning of periplasmic and outer membrane electron transport components. The exclusive presence of ompJ in members of the Geobacteraceae family as well as its role in metal reduction suggest that the ompJ sequence may be useful in tracking the growth or activity of Geobacteraceae in sedimentary environments.
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Affiliation(s)
- Eman Afkar
- Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003, USA
| | - Gemma Reguera
- Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003, USA
| | - Marianne Schiffer
- Biosciences Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - Derek R Lovley
- Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003, USA
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2766
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Frirdich E, Whitfield C. Characterization of Gla(KP), a UDP-galacturonic acid C4-epimerase from Klebsiella pneumoniae with extended substrate specificity. J Bacteriol 2005; 187:4104-15. [PMID: 15937173 PMCID: PMC1151718 DOI: 10.1128/jb.187.12.4104-4115.2005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
In Escherichia coli and Salmonella enterica, the core oligosaccharide backbone of the lipopolysaccharide is modified by phosphoryl groups. The negative charges provided by these residues are important in maintaining the barrier function of the outer membrane. In contrast, Klebsiella pneumoniae lacks phosphoryl groups in its core oligosaccharide but instead contains galacturonic acid residues that are proposed to serve a similar function in outer membrane stability. Gla(KP) is a UDP-galacturonic acid C4-epimerase that provides UDP-galacturonic acid for core synthesis, and the enzyme was biochemically characterized because of its potentially important role in outer membrane stability. High-performance anion-exchange chromatography was used to demonstrate the UDP-galacturonic acid C4-epimerase activity of Gla(KP), and capillary electrophoresis was used for activity assays. The reaction equilibrium favors UDP-galacturonic acid over UDP-glucuronic acid in a ratio of 1.4:1, with the K(m) for UDP-glucuronic acid of 13.0 microM. Gla(KP) exists as a dimer in its native form. NAD+/NADH is tightly bound by the enzyme and addition of supplementary NAD+ is not required for activity of the purified enzyme. Divalent cations have an unexpected inhibitory effect on enzyme activity. Gla(KP) was found to have a broad substrate specificity in vitro; it is capable of interconverting UDP-glucose/UDP-galactose and UDP-N-acetylglucosamine/UDP-N-acetylgalactosamine, albeit at much lower activity. The epimerase GalE interconverts UDP-glucose/UDP-galactose. Multicopy plasmid-encoded gla(KP) partially complemented a galE mutation in S. enterica and in K. pneumoniae; however, chromosomal gla(KP) could not substitute for galE in a K. pneumoniae galE mutant in vivo.
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Affiliation(s)
- Emilisa Frirdich
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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2767
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Vorob’eva EV, Dmitrenok AS, Dmitrenok PS, Isakov VV, Krasikova IN, Solov’eva TF. The Structure of Uncommon Lipid A from the Marine Bacterium Marinomonas communis ATCC 27118T. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2005. [DOI: 10.1007/s11171-005-0050-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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2768
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De Spiegeleer P, Sermon J, Vanoirbeek K, Aertsen A, Michiels CW. Role of porins in sensitivity of Escherichia coli to antibacterial activity of the lactoperoxidase enzyme system. Appl Environ Microbiol 2005; 71:3512-8. [PMID: 16000755 PMCID: PMC1169026 DOI: 10.1128/aem.71.7.3512-3518.2005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Accepted: 01/24/2005] [Indexed: 11/20/2022] Open
Abstract
Lactoperoxidase is an enzyme that contributes to the antimicrobial defense in secretory fluids and that has attracted interest as a potential biopreservative for foods and other perishable products. Its antimicrobial activity is based on the formation of hypothiocyanate (OSCN-) from thiocyanate (SCN-), using H2O2 as an oxidant. To gain insight into the antibacterial mode of action of the lactoperoxidase enzyme system, we generated random transposon insertion mutations in Escherichia coli MG1655 and screened the resultant mutants for an altered tolerance of bacteriostatic concentrations of this enzyme system. Out of the ca. 5,000 mutants screened, 4 showed significantly increased tolerance, and 2 of these had an insertion, one in the waaQ gene and one in the waaO gene, whose products are involved in the synthesis of the core oligosaccharide moiety of lipopolysaccharides. Besides producing truncated lipopolysaccharides and displaying hypersensitivity to novobiocin and sodium dodecyl sulfate (SDS), these mutants were also shown by urea-SDS-polyacrylamide gel electrophoresis analysis to have reduced amounts of porins in their outer membranes. Moreover, they showed a reduced degradation of p-nitrophenyl phosphate and an increased resistance to ampicillin, two indications of a decrease in outer membrane permeability for small hydrophilic solutes. Additionally, ompC and ompF knockout mutants displayed levels of tolerance to the lactoperoxidase system similar to those displayed by the waa mutants. These results suggest that mutations which reduce the porin-mediated outer membrane permeability for small hydrophilic molecules lead to increased tolerance to the lactoperoxidase enzyme system because of a reduced uptake of OSCN-.
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Affiliation(s)
- Philipp De Spiegeleer
- Department of Food and Microbial Technology, K.U. Leuven, Laboratory of Food Microbiology, Kasteelpark Arenberg 22, B-3001 Leuven, Belgium
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2769
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Doerrler WT, Raetz CRH. Loss of outer membrane proteins without inhibition of lipid export in an Escherichia coli YaeT mutant. J Biol Chem 2005; 280:27679-87. [PMID: 15951436 DOI: 10.1074/jbc.m504796200] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Escherichia coli yaeT encodes an essential, conserved outer membrane (OM) protein that is an ortholog of Neisseria meningitidis Omp85. Conflicting data with N. meningitidis indicate that Omp85 functions either in assembly of OM proteins or in export of OM lipids. The role of YaeT in E. coli was investigated with a new temperature-sensitive mutant harboring nine amino acid substitutions. The mutant stops growing after 60 min at 44 degrees C. After 30 min at 44 degrees C, incorporation of [35S]methionine into newly synthesized OM proteins is selectively inhibited. Synthesis and export of OM phospholipids and lipopolysaccharide are not impaired. OM protein levels are low, even at 30 degrees C, and the buoyant density of the OM is correspondingly lower. By Western blotting, we show that levels of the major OM protein OmpA are lower in the mutant in whole cells, membranes, and the growth medium. SecA functions as a multicopy suppressor of the temperature-sensitive phenotype and partially restores OM proteins. Our data are consistent with a critical role for YaeT in OM protein assembly in E. coli.
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Affiliation(s)
- William T Doerrler
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA
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2770
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Frirdich E, Bouwman C, Vinogradov E, Whitfield C. The role of galacturonic acid in outer membrane stability in Klebsiella pneumoniae. J Biol Chem 2005; 280:27604-12. [PMID: 15929980 DOI: 10.1074/jbc.m504987200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In most members of the Enterobacteriaceae, including Escherichia coli and Salmonella, the lipopolysaccharide core oligosaccharide backbone is modified by phosphoryl groups. The negative charges provided by these residues are important in maintaining the barrier function of the outer membrane. Mutants lacking the core heptose region and the phosphate residues display pleiotrophic defects collectively known as the deep-rough phenotype, characterized by changes in outer membrane structure and function. Klebsiella pneumoniae lacks phosphoryl residues in its core, but instead contains galacturonic acid. The goal of this study was to determine the contribution of galacturonic acid as a critical source of negative charge. A mutant was created lacking all galacturonic acid by targeting UDP-galacturonic acid precursor synthesis through a mutation in gla(KP). Gla(KP) is a K. pneumoniae UDP-galacturonic acid C4 epimerase providing UDP-galacturonic acid for core synthesis. The gla(KP) gene was inactivated and the structure of the mutant lipopolysaccharide was determined by mass spectrometry. The mutant displayed characteristics of a deep-rough phenotype, exhibiting a hypersensitivity to hydrophobic compounds and polymyxin B, an altered outer membrane profile, and the release of the periplasmic enzyme beta-lactamase. These results indicate that the negative charge provided by the carboxyl groups of galacturonic acid do play an equivalent role to the core oligosaccharide phosphate residues in establishing outer membrane integrity in E. coli and Salmonella.
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Affiliation(s)
- Emilisa Frirdich
- Department of Molecular and Cellular Biology, University of Guelph, Guelph Ontario N1G 2W1, Canada
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2771
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Walker SL, Hill JE, Redman JA, Elimelech M. Influence of growth phase on adhesion kinetics of Escherichia coli D21g. Appl Environ Microbiol 2005; 71:3093-9. [PMID: 15933006 PMCID: PMC1151849 DOI: 10.1128/aem.71.6.3093-3099.2005] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2004] [Accepted: 12/15/2004] [Indexed: 11/20/2022] Open
Abstract
The influence of bacterial growth stage and the evolution of surface macromolecules on cell adhesion have been examined by using a mutant of Escherichia coli K-12. To better understand the adhesion kinetics of bacteria in the mid-exponential and stationary growth phases under flow conditions, deposition experiments were conducted in a well-controlled radial stagnation point flow (RSPF) system. Complementary cell characterization techniques were conducted in combination with the RSPF experiments to evaluate the hydrophobicity, electrophoretic mobility, size, and titratable surface charge of the cells in the two growth phases considered. It was observed that cells in stationary phase were notably more adhesive than those in mid-exponential phase. This behavior is attributed to the high degree of local charge heterogeneity on the outer membranes of stationary-phase cells, which results in decreased electrostatic repulsion between the cells and a quartz surface. The mid-exponential-phase cells, on the other hand, have a more uniform charge distribution on the outer membrane, resulting in greater electrostatic repulsion and, subsequently, less adhesion. Our results suggest that the macromolecules responsible for this phenomenon are outer membrane-bound proteins and lipopolysaccharide-associated functional groups.
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Affiliation(s)
- Sharon L Walker
- Department of Chemical and Environmental Engineering, University of California, Riverside, B355 Bourns Hall, Riverside, California 92521, USA.
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2772
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Ruiz N, Falcone B, Kahne D, Silhavy TJ. Chemical conditionality: a genetic strategy to probe organelle assembly. Cell 2005; 121:307-17. [PMID: 15851036 DOI: 10.1016/j.cell.2005.02.014] [Citation(s) in RCA: 240] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2004] [Revised: 02/03/2005] [Accepted: 02/10/2005] [Indexed: 11/16/2022]
Abstract
The assembly of the Escherichia coli outer membrane (OM) is poorly understood. Although insight into fundamental cellular processes is often obtained from studying mutants, OM-defective mutants have not been very informative because they generally have nonspecific permeability defects. Here we show that toxic small molecules can be used in selections employing strains with permeability defects to create particular chemical conditions that demand specific suppressor mutations. Suppressor phenotypes are correlated with the physical properties of the small molecules, but the mutations are not in their target genes. Instead, mutations allow survival by partially restoring membrane impermeability. Using "chemical conditionality," we identified mutations in yfgL, and, here and in the accompanying paper by Wu et al. published in this issue of Cell (Wu et al., 2005), we show that YfgL is part of a multiprotein complex involved in the assembly of OM beta barrel proteins. We posit that panels of toxic small molecules will be useful for generating chemical conditionalities that enable identification of genes required for organelle assembly in other organisms.
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Affiliation(s)
- Natividad Ruiz
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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2773
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Wu T, Malinverni J, Ruiz N, Kim S, Silhavy TJ, Kahne D. Identification of a multicomponent complex required for outer membrane biogenesis in Escherichia coli. Cell 2005; 121:235-45. [PMID: 15851030 DOI: 10.1016/j.cell.2005.02.015] [Citation(s) in RCA: 570] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2004] [Revised: 02/03/2005] [Accepted: 02/10/2005] [Indexed: 11/16/2022]
Abstract
Gram-negative bacteria have an outer membrane (OM) that functions as a barrier to protect the cell from toxic compounds such as antibiotics and detergents. The OM is a highly asymmetric bilayer composed of phospholipids, glycolipids, and proteins. Assembly of this essential organelle occurs outside the cytoplasm in an environment that lacks obvious energy sources such as ATP, and the mechanisms involved are poorly understood. We describe the identification of a multiprotein complex required for the assembly of proteins in the OM of Escherichia coli. We also demonstrate genetic interactions between genes encoding components of this protein assembly complex and imp, which encodes a protein involved in the assembly of lipopolysaccharides (LPS) in the OM. These genetic interactions suggest a role for YfgL, one of the lipoprotein components of the protein assembly complex, in a homeostatic control mechanism that coordinates the overall OM assembly process.
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Affiliation(s)
- Tao Wu
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
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2774
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Affiliation(s)
- Amy L Davidson
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030, USA.
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2775
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Schild S, Lamprecht AK, Reidl J. Molecular and functional characterization of O antigen transfer in Vibrio cholerae. J Biol Chem 2005; 280:25936-47. [PMID: 15908430 DOI: 10.1074/jbc.m501259200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The majority of Gram-negative bacteria transfer O antigen polysaccharides onto the lipid A-core oligosaccharide via the action of surface polymer:lipid A-core ligases (WaaL). Here, we characterize the WaaL proteins of Vibrio cholerae with emphasis on structural and functional characterization of O antigen transfer and core oligosaccharide recognition. We demonstrate that the activity of two distantly related O antigen ligases is dependent on the presence of N-acetylglucosamine, and substitution of an additional sugar, i.e. galactose, alters the site specificity of the core oligosaccharide necessitating discriminative WaaL types. Protein topology analysis and a conserved domain search identified two distinct conserved motifs in the periplasmic domains of WaaL proteins. Site-directed mutagenesis of the two motifs, shown for WaaLs of V. cholerae and Salmonella enterica, caused a loss of O antigen transfer activity. Moreover, analogy of topology and motifs between WaaLs and O polysaccharide polymerases (Wzy) reveals a relationship between the two protein families, suggesting that the catalyzed reactions are related to each other.
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Affiliation(s)
- Stefan Schild
- Institut für Hygiene und Mikrobiologie, Universität Würzburg, Josef Schneider Strasse 2, E1, Würzburg 97080, Germany
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2776
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Daugelavicius R, Cvirkaite V, Gaidelyte A, Bakiene E, Gabrenaite-Verkhovskaya R, Bamford DH. Penetration of enveloped double-stranded RNA bacteriophages phi13 and phi6 into Pseudomonas syringae cells. J Virol 2005; 79:5017-26. [PMID: 15795287 PMCID: PMC1069564 DOI: 10.1128/jvi.79.8.5017-5026.2005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Bacteriophages phi6 and phi13 are related enveloped double-stranded RNA viruses that infect gram-negative Pseudomonas syringae cells. phi6 uses a pilus as a receptor, and phi13 attaches to the host lipopolysaccharide. We compared the entry-related events of these two viruses, including receptor binding, envelope fusion, peptidoglycan penetration, and passage through the plasma membrane. The infection-related events are dependent on the multiplicity of infection in the case of phi13 but not with phi6. A temporal increase of host outer membrane permeability to lipophilic ions was observed from 1.5 to 4 min postinfection in both virus infections. This enhanced permeability period coincided with the fast dilution of octadecyl rhodamine B-labeled virus-associated lipid molecules. This result is in agreement with membrane fusion, and the presence of temporal virus-derived membrane patches on the outer membrane. Similar to phi6, phi13 contains a thermosensitive lytic enzyme involved in peptidoglycan penetration. The phage entry also caused a limited depolarization of the plasma membrane. Inhibition of host respiration considerably decreased the efficiency of irreversible virus binding and membrane fusion. An active role of cell energy metabolism in restoring the infection-induced defects in the cell envelope was also observed.
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Affiliation(s)
- Rimantas Daugelavicius
- Department of Biological and Environmental Sciences and Institute of Biotechnology, University of Helsinki, Helsinki, Finland
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2777
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Mussi MA, Limansky AS, Viale AM. Acquisition of resistance to carbapenems in multidrug-resistant clinical strains of Acinetobacter baumannii: natural insertional inactivation of a gene encoding a member of a novel family of beta-barrel outer membrane proteins. Antimicrob Agents Chemother 2005; 49:1432-40. [PMID: 15793123 PMCID: PMC1068641 DOI: 10.1128/aac.49.4.1432-1440.2005] [Citation(s) in RCA: 192] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The outer membrane proteins responsible for the influx of carbapenem beta-lactam antibiotics in the nonfermentative gram-negative pathogen Acinetobacter baumannii are still poorly characterized. Resistance to both imipenem and meropenem in multidrug-resistant clinical strains of A. baumannii is associated with the loss of a heat-modifiable 29-kDa outer membrane protein, designated CarO. The chromosomal locus containing the carO gene was cloned and characterized from different clinical isolates. Only one carO copy, present in a single transcriptional unit, was found in the A. baumannii genome. The carO gene encodes a polypeptide of 247 amino acid residues with a typical N-terminal signal sequence and a predicted transmembrane beta-barrel topology. Its absence from different carbapenem-resistant clinical isolates of A. baumannii resulted from the disruption of carO by distinct insertion elements. The overall data thus support the notion that CarO participates in the influx of carbapenem antibiotics in A. baumannii. Moreover, database searches identified the presence of carO homologs only in species of the genera Acinetobacter, Moraxella, and Psychrobacter, disclosing the existence of a novel family of outer membrane proteins restricted to the family Moraxellaceae of the class gamma-Proteobacteria.
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Affiliation(s)
- María A Mussi
- Instituto de Biología Molecular y Celular de Rosario (IBR, CONICET) and Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Argentina
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2778
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Siritapetawee J, Prinz H, Krittanai C, Suginta W. Expression and refolding of Omp38 from Burkholderia pseudomallei and Burkholderia thailandensis, and its function as a diffusion porin. Biochem J 2005; 384:609-17. [PMID: 15329048 PMCID: PMC1134147 DOI: 10.1042/bj20041102] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In the present paper, we describe cloning and expression of two outer membrane proteins, BpsOmp38 (from Burkholderia pseudomallei) and BthOmp38 (from Burkholderia thailandensis) lacking signal peptide sequences, using the pET23d(+) expression vector and Escherichia coli host strain Origami(DE3). The 38 kDa proteins, expressed as insoluble inclusion bodies, were purified, solubilized in 8 M urea, and then subjected to refolding experiments. As seen on SDS/PAGE, the 38 kDa band completely migrated to approximately 110 kDa when the purified monomeric proteins were refolded in a buffer system containing 10% (w/v) Zwittergent 3-14, together with a subsequent heating to 95 degrees C for 5 min. CD spectroscopy revealed that the 110 kDa proteins contained a predominant beta-sheet structure, which corresponded completely to the structure of the Omp38 proteins isolated from B. pseudomallei and B. thailandensis. Immunoblot analysis using anti-BpsOmp38 polyclonal antibodies and peptide mass analysis by MALDI-TOF (matrix-assisted laser-desorption ionization-time-of-flight) MS confirmed that the expressed proteins were BpsOmp38 and BthOmp38. The anti-BpsOmp38 antibodies considerably exhibited the inhibitory effects on the permeation of small sugars through the Omp38-reconstituted liposomes. A linear relation between relative permeability rates and M(r) of neutral sugars and charged antibiotics suggested strongly that the in vitro re-assembled Omp38 functioned fully as a diffusion porin.
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Affiliation(s)
- Jaruwan Siritapetawee
- *School of Biochemistry, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
| | - Heino Prinz
- †Max Planck Institut für Molekulare Physiologie, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
| | - Chartchai Krittanai
- ‡Institute of Molecular Biology and Genetics, Mahidol University, Salaya, Nakhon Pathom, 73170, Thailand
| | - Wipa Suginta
- *School of Biochemistry, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
- To whom correspondence should be addressed (email )
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2779
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Hooper DC. Efflux pumps and nosocomial antibiotic resistance: a primer for hospital epidemiologists. Clin Infect Dis 2005; 40:1811-7. [PMID: 15909271 DOI: 10.1086/430381] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2004] [Accepted: 03/07/2005] [Indexed: 12/28/2022] Open
Affiliation(s)
- David C Hooper
- Division of Infectious Diseases, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114-2696, USA.
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2780
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Skopková-Zarnayová M, Siebor E, Rovná D, Bujdáková H, Neuwirth C. Outer membrane protein profiles of clonally related Klebsiella pneumoniae isolates that differ in cefoxitin resistance. FEMS Microbiol Lett 2005; 243:197-203. [PMID: 15668019 DOI: 10.1016/j.femsle.2004.12.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2004] [Revised: 10/13/2004] [Accepted: 12/07/2004] [Indexed: 11/19/2022] Open
Abstract
Eleven genotypically related Klebsiella pneumoniae isolates were obtained from 11 patients. All isolates were resistant to third-generation cephalosporins due to the production of SHV-2a extended-spectrum beta-lactamase. Comparison of the outer membrane protein profiles revealed one isolate that lacked porins. This porin-deficient isolate was also resistant to cefoxitin (MIC 128 microg ml(-1)) and moxalactam (MIC 64 microg ml(-1)) and had elevated MIC of meropenem (2 microg ml(-1)) when compared to porin-expressing isolates (2-8, 4 and <0.06-0.125 microg ml(-1), respectively). Higher MICs, associated with loss of porins in outer membrane, were also observed for cefotaxime (4-8-fold), cefepime (>2-16-fold), ciprofloxacin (4-16-fold), imipenem and aztreonam (2-16-fold), but there was no significant difference among MICs of ceftazidime. The porin-deficient mutant was probably selected in vivo during ofloxacin therapy.
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Affiliation(s)
- Martina Skopková-Zarnayová
- Department of Microbiology and Virology, Comenius University, Mlynska dolina B-2, 845 15 Bratislava, Slovakia.
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2781
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Zakharian E, Reusch RN. Kinetics of Folding ofEscherichia coliOmpA from Narrow to Large Pore Conformation in a Planar Bilayer†. Biochemistry 2005; 44:6701-7. [PMID: 15850404 DOI: 10.1021/bi047278e] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The outer membrane protein of Escherichia coli, OmpA, is currently alleged to adopt two native conformations: a major two-domain conformer in which 171 N-terminal residues form a narrow eight beta-barrel pore and 154 C-terminal residues are in the periplasm and a minor one-domain conformer in which all 325 residues create a large pore. However, recent studies in planar bilayers indicate the conformation of OmpA is temperature-sensitive and that increasing temperature converts narrow pores to large pores. Here we examine the reversibility and kinetics of this transition for single OmpA molecules in planar bilayers of diphytanoylphosphatidylcholine (DPhPC). We find that the transition is irreversible. When temperatures are decreased, large pores close down, and when temperatures are stabilized they reopen in the large pore conformation, with gradually increasing open time. Large pores are converted to narrow pores only by denaturing agents. The transition from narrow to large pores requires temperatures >or= 26 degrees C and is a biphasic process with rates that rise steeply with temperature. The first phase, a flickering stepwise transition from a low-conductance to a high-conductance state requires approximately 7 h at 26 degrees C but only approximately 13 min at 42 degrees C, signifying an activation energy of 139 +/- 12 kJ/mol. This is followed by a gradual increase in conductance and open probability, interpreted as optimization of the large pore structure. The results indicate that the two-domain structure is a partially folded intermediate that is kinetically stable at lower temperatures and that mature fully folded OmpA is a large pore.
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Affiliation(s)
- E Zakharian
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824, USA
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2782
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Kawasaki K, Ernst RK, Miller SI. Inhibition of Salmonella enterica serovar Typhimurium lipopolysaccharide deacylation by aminoarabinose membrane modification. J Bacteriol 2005; 187:2448-57. [PMID: 15774888 PMCID: PMC1065228 DOI: 10.1128/jb.187.7.2448-2457.2005] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Salmonella enterica serovar Typhimurium remodels the lipid A component of lipopolysaccharide, a major component of the outer membrane, to survive within animals. The activation of the sensor kinase PhoQ in host environments increases the synthesis of enzymes that deacylate, palmitoylate, hydroxylate, and attach aminoarabinose to lipid A, also known as endotoxin. These modifications promote bacterial resistance to antimicrobial peptides and reduce the host recognition of lipid A by Toll-like receptor 4. The Salmonella lipid A 3-O-deacylase, PagL, is an outer membrane protein whose expression is regulated by PhoQ. In S. enterica serovar Typhimurium strains that had the ability to add aminoarabinose to lipid A, 3-O-deacylated lipid A species were not detected, despite the PhoQ induction of PagL protein expression. In contrast, strains defective for the aminoarabinose modification of lipid A demonstrated in vivo PagL activity, indicating that this membrane modification inhibited PagL's enzymatic activity. Since not all lipid A molecules are modified with aminoarabinose upon PhoQ activation, these results cannot be ascribed to the substrate specificity of PagL. PagL-dependent deacylation was detected in sonically disrupted membranes and membranes treated with the nonionic detergent n-octyl-beta-d-glucopyranoside, suggesting that perturbation of the intact outer membrane releases PagL from posttranslational inhibition by aminoarabinose-containing membranes. Taken together, these results suggest that PagL enzymatic deacylation is posttranslationally inhibited by membrane environments, which either sequester PagL from its substrate or alter its conformation.
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Affiliation(s)
- Kiyoshi Kawasaki
- Department of Microbiology, University of Washington, Health Sciences Building, K140, Box 357710, 1959 Pacific St. N.E., Seattle, WA 98195, USA
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2783
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Fisher JF, Meroueh SO, Mobashery S. Bacterial resistance to beta-lactam antibiotics: compelling opportunism, compelling opportunity. Chem Rev 2005; 105:395-424. [PMID: 15700950 DOI: 10.1021/cr030102i] [Citation(s) in RCA: 684] [Impact Index Per Article: 36.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Jed F Fisher
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
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2784
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Vidal S, Bredin J, Pagès JM, Barbe J. Beta-lactam screening by specific residues of the OmpF eyelet. J Med Chem 2005; 48:1395-400. [PMID: 15743183 DOI: 10.1021/jm049652e] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Beta-lactams use aqueous channels of porins to penetrate Gram-negative bacteria. The L3 loop of Escherichia coli OmpF porin is a key feature that actively contributes to both channel size and electrostatic properties. Acid residues D113, E117, and D121 are responsible for the negative part of the local electrostatic field on this loop. Two substitutions, D113A and D121A, located in the negatively charged cluster of the OmpF eyelet, increase the likelihood of producing bacteria susceptible to several beta-lactams. D113A substitution results in an increase in the ampicillin, cefoxitin, and ceftazidime susceptibility. Molecular modeling suggests that the charges harbored by the beta-lactam molecules interact with the charged residues located inside the porin eyelet.
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Affiliation(s)
- Stéphanie Vidal
- GERCTOP UMR6178 CNRS, IFR48, Faculté de Pharmacie, Université de la Méditerranée, 13385 Marseille Cedex 05, France
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2785
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Condemine G, Berrier C, Plumbridge J, Ghazi A. Function and expression of an N-acetylneuraminic acid-inducible outer membrane channel in Escherichia coli. J Bacteriol 2005; 187:1959-65. [PMID: 15743943 PMCID: PMC1064066 DOI: 10.1128/jb.187.6.1959-1965.2005] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Escherichia coli yjhA (renamed nanC) gene encodes a protein of the KdgM family of outer membrane-specific channels. It is transcribed divergently from fimB, a gene involved in the site-specific inversion of the region controlling transcription of the fimbrial structural genes but is separated from it by one of the largest intergenic regions in E. coli. We show that nanC expression is induced by N-acetylneuraminic acid and modulated by N-acetylglucosamine. This regulation occurs via the NanR and NagC regulators, which also control fimB expression. nanC expression is also activated by the regulators cyclic AMP-catabolite activator protein, OmpR, and CpxR. When the NanC protein was reconstituted into liposomes, it formed channels with a conductance of 450 pS at positive potential and 300 to 400 pS at negative potential in 800 mM KCl. The channels had a weak anionic selectivity. In an ompR background, where the general porins OmpF and OmpC are absent, NanC is required for growth of E. coli on N-acetylneuraminic acid as the sole carbon source. All these results suggest that NanC is an N-acetylneuraminic acid outer membrane channel protein.
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Affiliation(s)
- Guy Condemine
- Unité Microbiologie et Génétique, UMR-CNRS-INSA-UCB 5122, Villeurbanne, France.
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2786
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Ghosh AS, Young KD. Helical disposition of proteins and lipopolysaccharide in the outer membrane of Escherichia coli. J Bacteriol 2005; 187:1913-22. [PMID: 15743937 PMCID: PMC1064060 DOI: 10.1128/jb.187.6.1913-1922.2005] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In bacteria, several physiological processes once thought to be the products of uniformly dispersed reactions are now known to be highly asymmetric, with some exhibiting interesting geometric localizations. In particular, the cell envelope of Escherichia coli displays a form of subcellular differentiation in which peptidoglycan and outer membrane proteins at the cell poles remain stable for generations while material in the lateral walls is diluted by growth and turnover. To determine if material in the side walls was organized in any way, we labeled outer membrane proteins with succinimidyl ester-linked fluorescent dyes and then grew the stained cells in the absence of dye. Labeled proteins were not evenly dispersed in the envelope but instead appeared as helical ribbons that wrapped around the outside of the cell. By staining the O8 surface antigen of E. coli 2443 with a fluorescent derivative of concanavalin A, we observed a similar helical organization for the lipopolysaccharide (LPS) component of the outer membrane. Fluorescence recovery after photobleaching indicated that some of the outer membrane proteins remained freely diffusible in the side walls and could also diffuse into polar domains. On the other hand, the LPS O antigen was virtually immobile. Thus, the outer membrane of E. coli has a defined in vivo organization in which a subfraction of proteins and LPS are embedded in stable domains at the poles and along one or more helical ribbons that span the length of this gram-negative rod.
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Affiliation(s)
- Anindya S Ghosh
- Department of Microbiology and Immunology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58202-9037, USA
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2787
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Reynolds CM, Kalb SR, Cotter RJ, Raetz CRH. A phosphoethanolamine transferase specific for the outer 3-deoxy-D-manno-octulosonic acid residue of Escherichia coli lipopolysaccharide. Identification of the eptB gene and Ca2+ hypersensitivity of an eptB deletion mutant. J Biol Chem 2005; 280:21202-11. [PMID: 15795227 DOI: 10.1074/jbc.m500964200] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Addition of a phosphoethanolamine (pEtN) moiety to the outer 3-deoxy-D-manno-octulosonic acid (Kdo) residue of lipopolysaccharide (LPS) in WBB06, a heptose-deficient Escherichia coli mutant, occurs when cells are grown in 5-50 mM CaCl2 (Kanipes, M. I., Lin, S., Cotter, R. J., and Raetz, C. R. H. (2001) J. Biol. Chem. 276, 1156-1163). A Ca2+-induced, membrane-bound enzyme was responsible for the transfer of the pEtN unit to the Kdo domain. We now report the identification of the gene encoding the pEtN transferase. E. coli yhjW was cloned and overexpressed, because it is homologous to a putative pEtN transferase implicated in the modification of the beta-chain heptose residue of Neisseria meningitidis lipo-oligosaccharide (Mackinnon, F. G., Cox, A. D., Plested, J. S., Tang, C. M., Makepeace, K., Coull, P. A., Wright, J. C., Chalmers, R., Hood, D. W., Richards, J. C., and Moxon, E. R. (2002) Mol. Microbiol. 43, 931-943). In vitro assays with Kdo2-4'-[32P]lipid A as the acceptor showed that YhjW (renamed EptB) utilizes phosphatidylethanolamine in the presence of Ca2+ to transfer the pEtN group. Stoichiometric amounts of diacylglycerol were generated during the EptB-catalyzed transfer of pEtN to Kdo2-lipid A. EptB is an inner membrane protein of 574 amino acid residues with five predicted trans-membrane segments within its N-terminal region. An in-frame replacement of eptB with a kanamycin resistance cassette rendered E. coli WBB06 (but not wild-type W3110) hypersensitive to CaCl2 at 5 mM or higher. Ca2+ hypersensitivity was suppressed by excess Mg2+ in the medium or by restoring the LPS core of WBB06. The latter was achieved by reintroducing the waaC and waaF genes, which encode LPS heptosyl transferases I and II, respectively. Our data demonstrate that pEtN modification of the outer Kdo protected cells containing heptose-deficient LPS from damage by high concentrations of Ca2+. Based on its sequence similarity to EptA(PmrC), we propose that the active site of EptB faces the periplasmic surface of the inner membrane.
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Affiliation(s)
- C Michael Reynolds
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA
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2788
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Bezrukov SM, Krasilnikov OV, Yuldasheva LN, Berezhkovskii AM, Rodrigues CG. Field-dependent effect of crown ether (18-crown-6) on ionic conductance of alpha-hemolysin channels. Biophys J 2005; 87:3162-71. [PMID: 15507690 PMCID: PMC1304786 DOI: 10.1529/biophysj.104.044453] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Closing linear poly(ethylene glycol) (PEG) into a circular "crown" dramatically changes its dynamics in the alpha-hemolysin channel. In the electrically neutral crown ether (C2H4O)6, six ethylene oxide monomers are linked into a circle that gives the molecule ion-complexing capacity and increases its rigidity. As with linear PEG, addition of the crown to the membrane-bathing solution decreases the ionic conductance of the channel and generates additional conductance noise. However, in contrast to linear PEG, both the conductance reduction (reporting on crown partitioning into the channel pore) and the noise (reporting on crown dynamics in the pore) now depend on voltage strongly and nonmonotonically. Within the whole frequency range accessible in channel reconstitution experiments, the noise power spectrum is "white", showing that crown exchange between the channel and the bulk solution is fast. Analyzing these data in the framework of a Markovian two-state model, we are able to characterize the process quantitatively. We show that the lifetime of the crown in the channel reaches its maximum (a few microseconds) at about the same voltage (approximately 100 mV, negative from the side of protein addition) where the crown's reduction of the channel conductance is most pronounced. Our interpretation is that, because of its rigidity, the crown feels an effective steric barrier in the narrowest part of the channel pore. This barrier together with crown-ion complexing and resultant interaction with the applied field leads to behavior usually associated with voltage-dependent binding in the channel pore.
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Affiliation(s)
- Sergey M Bezrukov
- Laboratory of Physical and Structural Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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2789
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Fuller-Schaefer CA, Kadner RJ. Multiple extracellular loops contribute to substrate binding and transport by the Escherichia coli cobalamin transporter BtuB. J Bacteriol 2005; 187:1732-9. [PMID: 15716445 PMCID: PMC1064007 DOI: 10.1128/jb.187.5.1732-1739.2005] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Escherichia coli outer membrane TonB-dependent transporters for iron complexes and cobalamins recognize their multiple and diverse substrates with high specificity and affinity. The X-ray crystallographic structures of several transporters show that the substrate-binding surfaces are comprised of residues from the internal globular domain and multiple extracellular loops. The extracellular loops on the N-terminal half of the transmembrane beta-barrel of the cobalamin transporter BtuB participate in binding of the cofactor calcium atoms and undergo substantial conformation changes upon substrate binding. The functional relevance of the five C-terminal loops was examined by examining the effects of short in-frame deletions. Each loop contributed in different ways to the binding of BtuB substrates. Deletions in loops 7, 8, 9, and 11 strongly decreased cobalamin binding and transport, whereas deletions in loops 8, 9, and 10 affected binding and entry of phage BF23. None of the loops were essential for the action of colicin E1 or E3, which is consistent with the crystallographic observation that the colicin E3 receptor-binding domain can contact almost all of the loops. A deletion in loop 9 or 11 eliminated the ability of cobalamin to inhibit the action of colicin E1. These phenotypes show that there are multiple independent binding elements and point out similarities and differences in binding properties among the TonB-dependent transporters.
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2790
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Nagano K, Read EK, Murakami Y, Masuda T, Noguchi T, Yoshimura F. Trimeric structure of major outer membrane proteins homologous to OmpA in Porphyromonas gingivalis. J Bacteriol 2005; 187:902-11. [PMID: 15659668 PMCID: PMC545718 DOI: 10.1128/jb.187.3.902-911.2005] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The major outer membrane proteins Pgm6 (41 kDa) and Pgm7 (40 kDa) of Porphyromonas gingivalis ATCC 33277 are encoded by open reading frames pg0695 and pg0694, respectively, which form a single operon. Pgm6 and Pgm7 (Pgm6/7) have a high degree of similarity to Escherichia coli OmpA in the C-terminal region and are predicted to form eight-stranded beta-barrels in the N-terminal region. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Pgm6/7 appear as bands with apparent molecular masses of 40 and 120 kDa, with and without a reducing agent, suggesting a monomer and trimer, respectively. To verify the predicted trimeric structure and function of Pgm6/7, we constructed three mutants with pg0695, pg0694, or both deleted. The double mutant produced no Pgm6/7. The single-deletion mutants appeared to contain less Pgm7 and Pgm6 and to form homotrimers that migrated slightly faster (115 kDa) and slower (130 kDa), respectively, than wild-type Pgm6/7 under nonreducing conditions. N-terminal amino acid sequencing and mass spectrometry analysis of partially digested Pgm6/7 detected only fragments from Pgm6 and Pgm7. Two-dimensional, diagonal electrophoresis and chemical cross-linking experiments with or without a reducing agent clearly showed that Pgm6/7 mainly form stable heterotrimers via intermolecular disulfide bonds. Furthermore, growth retardation and arrest of the three mutants and increased permeability of their outer membranes indicated that Pgm6/7 play an important role in outer membrane integrity. Based on results of liposome swelling experiments, these proteins are likely to function as a stabilizer of the cell wall rather than as a major porin in this organism.
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Affiliation(s)
- Keiji Nagano
- Department of Microbiology, School of Dentistry, Aichi-Gakuin University, Nagoya, Aichi 464-8650, Japan
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2791
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Chimento DP, Kadner RJ, Wiener MC. Comparative structural analysis of TonB-dependent outer membrane transporters: Implications for the transport cycle. Proteins 2005; 59:240-51. [PMID: 15739205 DOI: 10.1002/prot.20416] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
TonB-dependent outer membrane transporters (TBDTs) transport organometallic substrates across the outer membranes of Gram-negative bacteria. Currently, structures of four different TBDTs have been determined by X-ray crystallography. TBDT structures consist of a 22-stranded beta-barrel enclosing a hatch domain. Structure-based sequence alignment of these four TBDTs indicates the presence of highly conserved motifs in both the hatch and barrel domains. The conserved motifs of the two domains are always in close proximity to each other and interact. We analyzed the very large interfaces between the barrel and hatch domains of TBDTs and compared their properties to those of other protein-protein interfaces. These interfaces are extensively hydrated. Most of the interfacial waters form hydrogen bonds to either the barrel or the hatch domain, with the remainder functioning as bridging waters in the interface. The hatch/barrel interfacial properties most resemble those of obligate transient protein complexes, suggesting that the interface is conducive to conformational change and/or movement of the hatch within the barrel. These results indicate that TBDTs can readily accommodate substantial conformational change and movement of their hatch domains during the active transport cycle. Also, these structural changes may require only modest forces exerted by the energy-coupling TonB protein upon the transporter.
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Affiliation(s)
- David P Chimento
- Department of Microbiology, University of Virginia, Charlottesville, Virginia, USA
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2792
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Georgopapadakou NH. β-Lactamase inhibitors: evolving compounds for evolving resistance targets. Expert Opin Investig Drugs 2005; 13:1307-18. [PMID: 15461559 DOI: 10.1517/13543784.13.10.1307] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The many and diverse beta-lactamases produced by bacteria, particularly by Gram-negative pathogens, are increasingly posing a serious threat to the clinical utility of beta-lactams. First-generation inhibitors (clavulanic acid, sulbactam, tazobactam) focus on Ambler class A enzymes. However, recent structural upgrades of class A beta-lactamases (e.g. TEM, SHV) have extended their spectrum (extended-spectrum beta-lactamases and carbapenemases [Sme, NMC-A, IMI-1]) and have brought about the possibility of beta-lactamase-inhibitor resistance. Furthermore, the mobilisation and spread of originally chromosomal class C enzymes (CMY, MIR), the growing clinical importance of class B enzymes (IMP, VIM), the emergence of inhibitor-resistant, broad spectrum class D (OXA) enzymes and the co-existence of different classes of beta-lactamases in the same pathogen have spurred research toward universal inhibitors. A complicating issue is target accessibility in Gram-negative bacteria, particularly in Enterobacter, Acinetobacter, Pseudomonas, Stenotrophomonas and other organisms, which is necessary in order for the inhibitor to synergise with vulnerable beta-lactam antibiotics. Several new, broad-spectrum inhibitors have emerged: cephem sulfones and oxapenems are upgrades of penam sulfones and oxapenams, respectively, with cephem sulfones possibly extending their inhibition to class B metallo-enzymes; and boronates and phosphonates are designed de novo, based on common structural and mechanistic features of serine beta-lactamases.
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2793
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Alcaraz A, Nestorovich EM, Aguilella-Arzo M, Aguilella VM, Bezrukov SM. Salting out the ionic selectivity of a wide channel: the asymmetry of OmpF. Biophys J 2005; 87:943-57. [PMID: 15298901 PMCID: PMC1304502 DOI: 10.1529/biophysj.104/043414] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Although the crystallographic structure of the bacterial porin OmpF has been known for a decade, the physical mechanisms of its ionic selectivity are still under investigation. We address this issue in a series of experiments with varied pH, salt concentrations, inverted salt gradient, and charged and uncharged lipids. Measuring reversal potential, we show that OmpF selectivity (traditionally regarded as slightly cationic) depends strongly on pH and salt concentration and is conditionally asymmetric, that is, the calculated selectivity is sensitive to the direction of salt concentration gradient. At neutral pH and subdecimolar salt concentrations the channel exhibits nearly ideal cation selectivity (t(G)(+)=0.98+/-0.01). Substituting neutral DPhPC with DPhPS, we demonstrate that the fixed charge of the host lipid has a small but measurable effect on the channel reversal potential. The available structural information allows for a qualitative explanation of our experimental findings. These findings now lead us to re-examine the ionization state of 102 titratable sites of the OmpF channel. Using standard methods of continuum electrostatics tailored to our particular purpose, we find the charge distribution in the channel as a function of solution acidity and relate the pH-dependent asymmetry in channel selectivity to the pH-dependent asymmetry in charge distribution. In an attempt to find a simple phenomenological description of our results, we also discuss different macroscopic models of electrodiffusion through large channels.
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Affiliation(s)
- Antonio Alcaraz
- Departamento de Ciencias Experimentales, Universidad Jaume I, Castellón, Spain
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2794
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Hari-Dass R, Shah C, Meyer DJ, Raynes JG. Serum amyloid A protein binds to outer membrane protein A of gram-negative bacteria. J Biol Chem 2005; 280:18562-7. [PMID: 15705572 DOI: 10.1074/jbc.m500490200] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Serum amyloid A (SAA) is the major acute phase protein in man and most mammals. We observed SAA binding to a surprisingly large number of Gram-negative bacteria, including Escherichia coli, Salmonella typhimurium, Shigella flexneri, Klebsiella pneumoniae, Vibrio cholerae, and Pseudomonas aeruginosa. The binding was found to be high affinity and rapid. Importantly, this binding was not inhibited by high density lipoprotein with which SAA is normally complexed in serum. Binding was also observed when bacteria were offered serum containing SAA. Ligand blots following SDS-PAGE or two-dimensional gels revealed two major ligands of 29 and 35 kDa that bound SAA when probing with radiolabeled SAA or SAA and monoclonal anti-SAA. Following fractionation the ligand was found in the outer membrane fraction of E. coli and was identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry to be outer membrane protein A (OmpA). OmpA-deficient E. coli did not bind SAA, and following purification of OmpA the protein retained binding activity. The ligands on other bacteria were likely to be homologues of OmpA because wild type, but not OprF-deficient, P. aeruginosa bound SAA.
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Affiliation(s)
- Ranjeeta Hari-Dass
- Immunology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom
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2795
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Zhang Z, Gosset G, Barabote R, Gonzalez CS, Cuevas WA, Saier MH. Functional interactions between the carbon and iron utilization regulators, Crp and Fur, in Escherichia coli. J Bacteriol 2005; 187:980-90. [PMID: 15659676 PMCID: PMC545712 DOI: 10.1128/jb.187.3.980-990.2005] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2004] [Accepted: 10/26/2004] [Indexed: 11/20/2022] Open
Abstract
In Escherichia coli, the ferric uptake regulator (Fur) controls expression of the iron regulon in response to iron availability while the cyclic AMP receptor protein (Crp) regulates expression of the carbon regulon in response to carbon availability. We here identify genes subject to significant changes in expression level in response to the loss of both Fur and Crp. Many iron transport genes and several carbon metabolic genes are subject to dual control, being repressed by the loss of Crp and activated by the loss of Fur. However, the sodB gene, encoding superoxide dismutase, and the aceBAK operon, encoding the glyoxalate shunt enzymes, show the opposite responses, being activated by the loss of Crp and repressed by the loss of Fur. Several other genes including the sdhA-D, sucA-D, and fumA genes, encoding key constituents of the Krebs cycle, proved to be repressed by the loss of both transcription factors. Finally, the loss of both Crp and Fur activated a heterogeneous group of genes under sigmaS control encoding, for example, the cyclopropane fatty acid synthase, Cfa, the glycogen synthesis protein, GlgS, the 30S ribosomal protein, S22, and the mechanosensitive channel protein, YggB. Many genes appeared to be regulated by the two transcription factors in an apparently additive fashion, but apparent positive or negative cooperativity characterized several putative Crp/Fur interactions. Relevant published data were evaluated, putative Crp and Fur binding sites were identified, and representative results were confirmed by real-time PCR. Molecular explanations for some, but not all, of these effects are provided.
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MESH Headings
- Bacterial Proteins/genetics
- Bacterial Proteins/metabolism
- Base Sequence
- Binding Sites
- Carbon/metabolism
- Cyclic AMP Receptor Protein
- DNA, Bacterial/chemistry
- DNA, Bacterial/genetics
- DNA, Bacterial/metabolism
- Escherichia coli/genetics
- Escherichia coli/growth & development
- Escherichia coli/metabolism
- Escherichia coli Proteins/genetics
- Escherichia coli Proteins/metabolism
- Gene Expression Regulation, Bacterial
- Gene Expression Regulation, Enzymologic
- Glucose/metabolism
- Iron/metabolism
- Kinetics
- Nucleic Acid Hybridization
- Phenotype
- Polymerase Chain Reaction
- RNA, Bacterial/genetics
- RNA, Bacterial/isolation & purification
- Receptors, Cell Surface/genetics
- Receptors, Cell Surface/metabolism
- Regulatory Sequences, Nucleic Acid
- Repressor Proteins/genetics
- Repressor Proteins/metabolism
- Transcription Factors/genetics
- Transcription Factors/metabolism
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Affiliation(s)
- Zhongge Zhang
- Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093-0116, USA
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2796
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Breazeale SD, Ribeiro AA, McClerren AL, Raetz CRH. A formyltransferase required for polymyxin resistance in Escherichia coli and the modification of lipid A with 4-Amino-4-deoxy-L-arabinose. Identification and function oF UDP-4-deoxy-4-formamido-L-arabinose. J Biol Chem 2005; 280:14154-67. [PMID: 15695810 DOI: 10.1074/jbc.m414265200] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Modification of the phosphate groups of lipid A with 4-amino-4-deoxy-L-arabinose (L-Ara4N) is required for resistance to polymyxin and cationic antimicrobial peptides in Escherichia coli and Salmonella typhimurium. We previously demonstrated that the enzyme ArnA catalyzes the NAD+-dependent oxidative decarboxylation of UDP-glucuronic acid to yield the UDP-4''-ketopentose, uridine 5'-diphospho-beta-(L-threo-pentapyranosyl-4''-ulose), which is converted by ArnB to UDP-beta-(L-Ara4N). E. coli ArnA is a bi-functional enzyme with a molecular mass of approximately 74 kDa. The oxidative decarboxylation of UDP-glucuronic acid is catalyzed by the 345-residue C-terminal domain of ArnA. The latter shows sequence similarity to enzymes that oxidize the C-4'' position of sugar nucleotides, like UDP-galactose epimerase, dTDP-glucose-4,6-dehydratase, and UDP-xylose synthase. We now show that the 304-residue N-terminal domain catalyzes the N-10-formyltetrahydrofolate-dependent formylation of the 4''-amine of UDP-L-Ara4N, generating the novel sugar nucleotide, uridine 5'-diphospho-beta-(4-deoxy-4-formamido-L-arabinose). The N-terminal domain is highly homologous to methionyl-tRNA(f)Met formyltransferase. The structure of the formylated sugar nucleotide generated in vitro by ArnA was validated by 1H and 13C NMR spectroscopy. The two domains of ArnA were expressed independently as active proteins in E. coli. Both were required for maintenance of polymyxin resistance and L-Ara4N modification of lipid A. We conclude that N-formylation of UDP-L-Ara4N is an obligatory step in the biosynthesis of L-Ara4N-modified lipid A in polymyxin-resistant mutants. We further demonstrate that only the formylated sugar nucleotide is converted in vitro to an undecaprenyl phosphate-linked form by the enzyme ArnC. Because the L-Ara4N unit attached to lipid A is not derivatized with a formyl group, we postulate the existence of a deformylase, acting later in the pathway.
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Affiliation(s)
- Steven D Breazeale
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA
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2797
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Murray SR, de Felipe KS, Obuchowski PL, Pike J, Bermudes D, Low KB. Hot spot for a large deletion in the 18- to 19-centisome region confers a multiple phenotype in Salmonella enterica serovar Typhimurium strain ATCC 14028. J Bacteriol 2005; 186:8516-23. [PMID: 15576802 PMCID: PMC532402 DOI: 10.1128/jb.186.24.8516-8523.2004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Loss of the Salmonella MsbB enzyme, which catalyzes the incorporation of myristate destined for lipopolysaccharide in the outer membrane, results in a strong phenotype of sensitivity to salt and chelators such as EGTA and greatly diminished endotoxic activity. MsbB- salmonellae mutate extragenically to EGTA-tolerant derivatives at a frequency of 10(-4) per division. One of these derivatives arose from inactivation of somA, which suppresses sensitivity to salt and EGTA. Here we show that a second mode of MsbB- suppression is a RecA-dependent deletion between two IS200 insertion elements present in Salmonella enterica serovar Typhimurium strain ATCC 14028 but not in two other wild-type strains, LT2 and SL1344, which lack one of the IS200 elements. This deletion occurs spontaneously in wild-type and MsbB- strain 14028 salmonellae and accounts for about one-third of all of the spontaneous suppressors of MsbB- in strain 14028. It spans the region corresponding to 17.7 to 19.9 centisomes, which includes somA, on the sequenced map of Salmonella LT2 (136 ORFs in that strain; ATCC 14028 and other strains showed variability in this region). In addition to conferring EGTA resistance correlated with somA, the deletion confers a MacConkey galactose resistance phenotype on MsbB- Salmonella, indicating that at least one additional gene (distinct from somA) within the deletion is responsible for this phenotype. In the wild type, the deletion mutant grows with normal exponential growth rate in Luria broth but is chlorate resistant and does not grow on citrate agar. The deletion strains have lost hydrogen sulfide production, nitrate reductase activity, and gas production from glucose fermentation.
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Affiliation(s)
- Sean R Murray
- Radiobiology Laboratories, Department of Therapeutic Radiology, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06520-8040, USA
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2798
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Lemieux MJ, Huang Y, Wang DN. Glycerol-3-phosphate transporter of Escherichia coli: structure, function and regulation. Res Microbiol 2005; 155:623-9. [PMID: 15380549 DOI: 10.1016/j.resmic.2004.05.016] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2004] [Accepted: 05/14/2004] [Indexed: 11/22/2022]
Abstract
Glycerol-3-phosphate (G3P) plays a major role in glycolysis and phospholipid biosynthesis in the cell. Escherichia coli uses a secondary membrane transporter protein, GlpT, to uptake G3P into the cytoplasm. The crystal structure of the protein was recently determined to 3.3 A resolution. The protein consists of an N- and a C-terminal domain, each formed by a compact bundle of six transmembrane alpha-helices. The substrate-translocation pore is found at the domain interface and faces the cytoplasm. At the closed end of the pore is the substrate binding site, which is formed by two arginine residues. In combination with biochemical data, the crystal structure suggests a single binding site, alternating access mechanism for substrate translocation, namely, the substrate bound at the N- and C-terminal domain interface is transported across the membrane via a rocker-switch type of movement of the domains. Furthermore, GlpT may serve as a structural and mechanistic paradigm for other secondary active membrane transporters.
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Affiliation(s)
- M Joanne Lemieux
- Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
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2799
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Ranquin A, Van Gelder P. Maltoporin: sugar for physics and biology. Res Microbiol 2005; 155:611-6. [PMID: 15380547 DOI: 10.1016/j.resmic.2004.05.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2004] [Accepted: 05/11/2004] [Indexed: 11/25/2022]
Abstract
Maltoporin has been studied for over 50 years. This trimeric bacterial outer membrane channel allows permeation of sugars such as maltodextrins. Its structure is described and functional studies resulting in a mechanistic transport model are critically discussed.
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Affiliation(s)
- An Ranquin
- Department of Molecular and Cellular Interactions, Free University of Brussels and Flanders Interuniversity Institute for Biotechnology (VIB), Pleinlaan 2, 1050 Brussels, Belgium
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2800
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Puupponen-Pimiä R, Nohynek L, Alakomi HL, Oksman-Caldentey KM. The action of berry phenolics against human intestinal pathogens. Biofactors 2005; 23:243-51. [PMID: 16498212 DOI: 10.1002/biof.5520230410] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Phenolic compounds present in berries selectively inhibit the growth of human gastrointestinal pathogens. Especially cranberry, cloudberry, raspberry, strawberry and bilberry possess clear antimicrobial effects against e.g. salmonella and staphylococcus. Complex phenolic polymers, such as ellagitannins, are strong antibacterial agents present in cloudberry, raspberry and strawberry. Berry phenolics seem to affect the growth of different bacterial species with different mechanisms. Adherence of bacteria to epithelial surfaces is a prerequisite for colonization and infection of many pathogens. Antimicrobial activity of berries may also be related to anti-adherence activity of the berries. Utilization of enzymes in berry processing increases the amount of phenolics and antimicrobial activity of the berry products. Antimicrobial berry compounds are likely to have many important applications in the future as natural antimicrobial agents for food industry as well as for medicine.
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