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Panji Z, Nadoushan MJ, Fekrirad Z, Rasooli I. Modulation with anti-Oma87 antibodies of cytotoxicity, adherence, and internalization of Acinetobacter baumannii in human cervical carcinoma epithelial cells. APMIS 2024. [PMID: 39223818 DOI: 10.1111/apm.13465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2024] [Accepted: 08/12/2024] [Indexed: 09/04/2024]
Abstract
BamA, an Omp85 superfamily member, is universally conserved and essential for cell viability. Using anti-Oma87 antibodies, we focus on understanding the effect of Oma87 of Acinetobacter baumannii on pathogenicity. Oma87 was expressed, purified, and used to induce anti-Oma87 antibodies in BALB/c mice. Acute toxicity of the protein was evaluated in mice. HeLa cells were infected with both live and killed A. baumannii 19606 and a clinical isolate. The effects of anti-Oma87 sera on A. baumannii adherence, internalization, and proliferation in HeLa cells were studied. The roles of microfilaments and microtubules in A. baumannii invasion were demonstrated by Actin disruption. Reduced bacterial population and biofilm formation were noted. The ability of A. baumannii to provoke autophagy through Oma87 induction leads to incomplete autophagy and potentially facilitates bacterial replication. Actin-mediated uptake, attachment, and invasion demonstrated A. baumannii survival and multiplication within vacuoles in the host cell. The findings underscore the potential of Oma87 as a therapeutic intervention target in infections caused by A. baumannii. This comprehensive analysis contributes valuable information for understanding the virulence mechanisms of A. baumannii, potentially guiding future strategies to combat infections caused by this pathogen.
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Affiliation(s)
- Zahra Panji
- Department of Biology, Shahed University, Tehran, Iran
| | - Mohammadreza Jalali Nadoushan
- Department of Pathology, School of Medicine, Shahed University, Tehran, Iran
- Molecular Microbiology Research Center and Department of Biology, Shahed University, Tehran, Iran
| | | | - Iraj Rasooli
- Department of Biology, Shahed University, Tehran, Iran
- Molecular Microbiology Research Center and Department of Biology, Shahed University, Tehran, Iran
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2
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Hall KT, Kenedy MR, Johnson DK, Hefty PS, Akins DR. A conserved C-terminal domain of TamB interacts with multiple BamA POTRA domains in Borreliella burgdorferi. PLoS One 2024; 19:e0304839. [PMID: 39208212 PMCID: PMC11361582 DOI: 10.1371/journal.pone.0304839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Accepted: 05/20/2024] [Indexed: 09/04/2024] Open
Abstract
Lyme disease is the leading tick-borne infection in the United States, caused by the pathogenic spirochete Borreliella burgdorferi, formerly known as Borrelia burgdorferi. Diderms, or bacteria with dual-membrane ultrastructure, such as B. burgdorferi, have multiple methods of transporting and integrating outer membrane proteins (OMPs). Most integral OMPs are transported through the β-barrel assembly machine (BAM) complex. This complex consists of the channel-forming OMP BamA and accessory lipoproteins that interact with the five periplasmic, polypeptide transport-associated (POTRA) domains of BamA. Another system, the translocation and assembly module (TAM) system, has also been implicated in OMP assembly and export. The TAM system consists of two proteins, the BamA paralog TamA which has three POTRA domains and the inner membrane protein TamB. TamB is characterized by a C-terminal DUF490 domain that interacts with the POTRA domains of TamA. Interestingly, while TamB is found in almost all diderms, including B. burgdorferi, TamA is found almost exclusively in Proteobacteria. This strongly suggests a TamA-independent role of TamB in most diderms. We previously demonstrated that BamA interacts with TamB in B. burgdorferi and hypothesized that this is facilitated by the BamA POTRA domains interacting with the TamB DUF490 domain. In this study, we utilized protein-protein co-purification assays to empirically demonstrate that the B. burgdorferi TamB DUF490 domain interacts with BamA POTRA2 and POTRA3. We also observed that the DUF490 domain of TamB interacts with the accessory lipoprotein BamB. To examine if the BamA-TamB interaction is more ubiquitous among diderms, we examined BamA-TamB interactions in Salmonella enterica serovar Typhimurium (St). Interestingly, even though St encodes a TamA protein that interacts with TamB, we observed that the TamB DUF490 of St interacts with BamA in this organism. Our combined findings strongly suggest that the TamB-BamA interaction occurs independent of the TamA component of the TAM protein export system.
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Affiliation(s)
- Kari T. Hall
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America
| | - Melisha R. Kenedy
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America
| | - David K. Johnson
- Chemical Computational Biology Core and the Molecular Graphics and Modeling Laboratory, University of Kansas, Lawrence, Kansas, United States of America
| | - P. Scott Hefty
- Department of Molecular Biosciences and the Center for Chemical Biology of Infectious Disease, University of Kansas, Lawrence, Kansas, United States of America
| | - Darrin R. Akins
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America
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3
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Gerken H, Shetty D, Kern B, Kenney LJ, Misra R. Effects of pleiotropic ompR and envZ alleles of Escherichia coli on envelope stress and antibiotic sensitivity. J Bacteriol 2024; 206:e0017224. [PMID: 38809006 PMCID: PMC11332150 DOI: 10.1128/jb.00172-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Accepted: 05/06/2024] [Indexed: 05/30/2024] Open
Abstract
The EnvZ-OmpR two-component system of Escherichia coli regulates the expression of the ompF and ompC porin genes in response to medium osmolarity. However, certain mutations in envZ confer pleiotropy by affecting the expression of genes of the iron and maltose regulons not normally controlled by EnvZ-OmpR. In this study, we obtained two novel envZ and ompR pleiotropic alleles, envZT15P and ompRL19Q, among revertants of a mutant with heightened envelope stress and an outer membrane (OM) permeability defect. Unlike envZ, pleiotropic mutations in ompR have not been described previously. The mutant alleles reduced the expression of several outer membrane proteins (OMPs), overcame the temperature-sensitive growth defect of a protease-deficient (ΔdegP) strain, and lowered envelope stress and OM permeability defects in a background lacking the BamB protein of an essential β-barrel assembly machinery complex. Biochemical analysis showed OmpRL19Q, like wild-type OmpR, is readily phosphorylated by EnvZ, but the EnvZ-dependent dephosphorylation of OmpRL19Q~P was drastically impaired compared to wild-type OmpR. This defect would lead to a prolonged half-life for OmpRL19Q~P, an outcome remarkably similar to what we had previously described for EnvZR397L, resulting in pleiotropy. By employing null alleles of the OMP genes, it was determined that the three pleiotropic alleles lowered envelope stress by reducing OmpF and LamB levels. The absence of LamB was principally responsible for lowering the OM permeability defect, as assessed by the reduced sensitivity of a ΔbamB mutant to vancomycin and rifampin. Possible mechanisms by which novel EnvZ and OmpR mutants influence EnvZ-OmpR interactions and activities are discussed.IMPORTANCEMaintenance of the outer membrane (OM) integrity is critical for the survival of Gram-negative bacteria. Several envelope homeostasis systems are activated when OM integrity is perturbed. Through the isolation and characterization of novel pleiotropic ompR/envZ alleles, this study highlights the involvement of the EnvZ-OmpR two-component system in lowering envelope stress and the OM permeability defect caused by the loss of proteins that are involved in OM biogenesis, envelope homeostasis, and structural integrity.
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Affiliation(s)
- Henri Gerken
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Dasvit Shetty
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, Texas, USA
| | - Brea Kern
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Linda J. Kenney
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, Texas, USA
- Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch at Galveston, Galveston, Texas, USA
| | - Rajeev Misra
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
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4
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He F, Xiong P, Zhang H, Yang L, Qiu Y, Li P, Zhao G, Li N, Peng Y. Attenuated vaccine PmCQ2Δ4555-4580 effectively protects mice against Pasteurella multocida infection. BMC Vet Res 2024; 20:94. [PMID: 38461234 PMCID: PMC10924365 DOI: 10.1186/s12917-024-03948-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Accepted: 02/20/2024] [Indexed: 03/11/2024] Open
Abstract
Pasteurella multocida type A (PmA) mainly causes respiratory diseases such as pneumonia in bovines, leading to great economic losses to the breeding industry. At present, there is still no effective commercial vaccine against PmA infection. In this study, a mutant strain (PmCQ2Δ4555-4580) with brand-new phenotypes was obtained after serially passaging at 42 °C. Whole genome resequencing and PCR analysis showed that PmCQ2Δ4555-4580 missed six genes, including PmCQ2_004555, PmCQ2_004560, PmCQ2_004565, PmCQ2_004570, PmCQ2_004575, and PmCQ2_004580. Importantly, the virulence of PmCQ2Δ4555-4580 was reduced by approximately 2.8 × 109 times in mice. Notably, live PmCQ2Δ4555-4580 could provide 100%, 100% and 40% protection against PmA, PmB and PmF, respectively; and inactivated PmCQ2Δ4555-4580 could provide 100% and 87.5% protection against PmA and PmB. Interestingly, immune protection-related proteins were significantly upregulated in PmCQ2Δ4555-4580 based on RNA-seq and bioinformatics analysis. Meaningfully, by in vitro expression, purification and in vivo immunization, 12 proteins had different degrees of immune protective effects. Among them, PmCQ2_008205, PmCQ2_010435, PmCQ2_008190, and PmCQ2_004170 had the best protective effect, the protection rates against PmA were 50%, 40%, 30%, and 30%, respectively, and the protective rates against PmB were 62.5%, 42.9%, 37.5%, and 28.6%, respectively. Collectively, PmCQ2Δ4555-4580 is a potential vaccine candidate for the prevention of Pasteurellosis involving in high expression of immune protective related proteins.
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Affiliation(s)
- Fang He
- College of Veterinary Medicine, Southwest University, Chongqing, 400715, China
| | - Pan Xiong
- College of Veterinary Medicine, Southwest University, Chongqing, 400715, China
| | - Huihui Zhang
- College of Veterinary Medicine, Southwest University, Chongqing, 400715, China
| | - Liu Yang
- College of Veterinary Medicine, Southwest University, Chongqing, 400715, China
| | - Yangyang Qiu
- College of Veterinary Medicine, Southwest University, Chongqing, 400715, China
| | - Pan Li
- Department of Environment and Safety Engineering, Taiyuan institute of technology, Taiyuan, 030008, China
| | - Guangfu Zhao
- College of Veterinary Medicine, Southwest University, Chongqing, 400715, China
| | - Nengzhang Li
- College of Veterinary Medicine, Southwest University, Chongqing, 400715, China.
| | - Yuanyi Peng
- College of Veterinary Medicine, Southwest University, Chongqing, 400715, China.
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5
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George A, Patil AG, Mahalakshmi R. ATP-independent assembly machinery of bacterial outer membranes: BAM complex structure and function set the stage for next-generation therapeutics. Protein Sci 2024; 33:e4896. [PMID: 38284489 PMCID: PMC10804688 DOI: 10.1002/pro.4896] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 12/28/2023] [Accepted: 12/31/2023] [Indexed: 01/30/2024]
Abstract
Diderm bacteria employ β-barrel outer membrane proteins (OMPs) as their first line of communication with their environment. These OMPs are assembled efficiently in the asymmetric outer membrane by the β-Barrel Assembly Machinery (BAM). The multi-subunit BAM complex comprises the transmembrane OMP BamA as its functional subunit, with associated lipoproteins (e.g., BamB/C/D/E/F, RmpM) varying across phyla and performing different regulatory roles. The ability of BAM complex to recognize and fold OM β-barrels of diverse sizes, and reproducibly execute their membrane insertion, is independent of electrochemical energy. Recent atomic structures, which captured BAM-substrate complexes, show the assembly function of BamA can be tailored, with different substrate types exhibiting different folding mechanisms. Here, we highlight common and unique features of its interactome. We discuss how this conserved protein complex has evolved the ability to effectively achieve the directed assembly of diverse OMPs of wide-ranging sizes (8-36 β-stranded monomers). Additionally, we discuss how darobactin-the first natural membrane protein inhibitor of Gram-negative bacteria identified in over five decades-selectively targets and specifically inhibits BamA. We conclude by deliberating how a detailed deduction of BAM complex-associated regulation of OMP biogenesis and OM remodeling will open avenues for the identification and development of effective next-generation therapeutics against Gram-negative pathogens.
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Affiliation(s)
- Anjana George
- Molecular Biophysics Laboratory, Department of Biological SciencesIndian Institute of Science Education and ResearchBhopalIndia
| | - Akanksha Gajanan Patil
- Molecular Biophysics Laboratory, Department of Biological SciencesIndian Institute of Science Education and ResearchBhopalIndia
| | - Radhakrishnan Mahalakshmi
- Molecular Biophysics Laboratory, Department of Biological SciencesIndian Institute of Science Education and ResearchBhopalIndia
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6
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Gopinath A, Rath T, Morgner N, Joseph B. Lateral gating mechanism and plasticity of the β-barrel assembly machinery complex in micelles and Escherichia coli. PNAS NEXUS 2024; 3:pgae019. [PMID: 38312222 PMCID: PMC10833450 DOI: 10.1093/pnasnexus/pgae019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Accepted: 01/08/2024] [Indexed: 02/06/2024]
Abstract
The β-barrel assembly machinery (BAM) mediates the folding and insertion of the majority of outer membrane proteins (OMPs) in gram-negative bacteria. BAM is a penta-heterooligomeric complex consisting of the central β-barrel BamA and four interacting lipoproteins BamB, C, D, and E. The conformational switching of BamA between inward-open (IO) and lateral-open (LO) conformations is required for substrate recognition and folding. However, the mechanism for the lateral gating or how the structural details observed in vitro correspond with the cellular environment remains elusive. In this study, we addressed these questions by characterizing the conformational heterogeneity of BamAB, BamACDE, and BamABCDE complexes in detergent micelles and/or Escherichia coli using pulsed dipolar electron spin resonance spectroscopy (PDS). We show that the binding of BamB does not induce any visible changes in BamA, and the BamAB complex exists in the IO conformation. The BamCDE complex induces an IO to LO transition through a coordinated movement along the BamA barrel. However, the extracellular loop 6 (L6) is unaffected by the presence of lipoproteins and exhibits large segmental dynamics extending to the exit pore. PDS experiments with the BamABCDE complex in intact E. coli confirmed the dynamic behavior of both the lateral gate and the L6 in the native environment. Our results demonstrate that the BamCDE complex plays a key role in the function by regulating lateral gating in BamA.
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Affiliation(s)
- Aathira Gopinath
- Department of Physics, Freie Universität Berlin, Berlin, 14195, Germany
- Institute of Biophysics, Goethe Universität Frankfurt, Frankfurt, 60438, Germany
| | - Tobias Rath
- Institute of Physical and Theoretical Chemistry, Goethe Universität Frankfurt, Frankfurt, 60438, Germany
| | - Nina Morgner
- Institute of Physical and Theoretical Chemistry, Goethe Universität Frankfurt, Frankfurt, 60438, Germany
| | - Benesh Joseph
- Department of Physics, Freie Universität Berlin, Berlin, 14195, Germany
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7
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Liu L, Tang S, Liu T, Zhang Z, Wang X, Bilal M, Liu S, Luo H, Zhao Y, Duan X. Transcriptomic analysis approach towards an improved tolerance of Escherichia coli to gallic acid stress. Arch Microbiol 2023; 205:372. [PMID: 37934297 DOI: 10.1007/s00203-023-03708-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Revised: 10/01/2023] [Accepted: 10/13/2023] [Indexed: 11/08/2023]
Abstract
As a natural green additive, gallic acid has been widely used in food production. However, it can inhibit the physiological metabolism of Escherichia coli, which severely limits the ability and efficiency of gallic acid production. To explore the adaptation mechanism of E. coli under gallic acid stress and further explore the target of genetic modification, the effects of gallic acid stress on the fermentation characteristics of E. coli W3110 ATCC (82057) were investigated by cell biomass and cell morphometry. Moreover, transcriptome analysis was used to analyze the gene transcription level of E. coli W3110 ATCC (82057) to explore effects of gallic acid stress on important essential physiological processes. The results showed that under high concentration of gallic acid, the biomass of E. coli W3110 ATCC (82057) decreased significantly and the cells showed irregular morphology. Transcriptome analysis showed that E. coli W3110 ATCC (82057) improved its adaptive capacity through three strategies. First, genes of bamD, ompC, and ompF encoding outer membrane protein BamD, OmpC, and OmpC were decreased 5-, 31.1- and 8.1-fold, respectively, under gallic acid stress compared to the control, leading to the reduction of gallic acid absorption. Moreover, genes (mdtA, mdtB, mdtC, mdtD, mdtE, and mdtF) related to MdtABC multidrug efflux system and multidrug efflux pump MdtEF were up-regulated by1.0-53.0 folds, respectively, and genes (aaeA, aaeB, and aaeX) related to AaeAB efflux system were up-regulated by 8.0-13.3 folds, respectively, which contributed to the excretion of gallic acid. In addition, genes of acid fitness island also were up-regulated by different degrees under the stress of an acidic environment to maintain the stability of the intracellular environment. In conclusion, E. coli W3110 ATCC (82057) would enhance its tolerance to gallic acid by reducing absorption, increasing excretion, and maintaining intracellular environment stability. This study provides research ideas for the construction of engineered strains with high gallic acid yield.
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Affiliation(s)
- Lina Liu
- School of Life Science and Food Engineering, Huaiyin Institute of Technology, Huaian, 223003, China.
| | - Shijie Tang
- School of Life Science and Food Engineering, Huaiyin Institute of Technology, Huaian, 223003, China
| | - Tingting Liu
- School of Life Science and Food Engineering, Huaiyin Institute of Technology, Huaian, 223003, China
| | - Zihao Zhang
- School of Life Science and Food Engineering, Huaiyin Institute of Technology, Huaian, 223003, China
| | - Xuefeng Wang
- School of Life Science and Food Engineering, Huaiyin Institute of Technology, Huaian, 223003, China
| | - Muhammad Bilal
- School of Life Science and Food Engineering, Huaiyin Institute of Technology, Huaian, 223003, China
| | - Shuai Liu
- School of Life Science and Food Engineering, Huaiyin Institute of Technology, Huaian, 223003, China
| | - Hongzhen Luo
- School of Life Science and Food Engineering, Huaiyin Institute of Technology, Huaian, 223003, China
| | - Yuping Zhao
- School of Life Science and Food Engineering, Huaiyin Institute of Technology, Huaian, 223003, China
| | - Xuguo Duan
- College of Light Industry and Food Engineering, Nanjing Forestry University, Nanjing, 210037, Jiangsu, China
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8
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Tassinari M, Rudzite M, Filloux A, Low HH. Assembly mechanism of a Tad secretion system secretin-pilotin complex. Nat Commun 2023; 14:5643. [PMID: 37704603 PMCID: PMC10499894 DOI: 10.1038/s41467-023-41200-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 08/25/2023] [Indexed: 09/15/2023] Open
Abstract
The bacterial Tight adherence Secretion System (TadSS) assembles surface pili that drive cell adherence, biofilm formation and bacterial predation. The structure and mechanism of the TadSS is mostly unknown. This includes characterisation of the outer membrane secretin through which the pilus is channelled and recruitment of its pilotin. Here we investigate RcpA and TadD lipoprotein from Pseudomonas aeruginosa. Light microscopy reveals RcpA colocalising with TadD in P. aeruginosa and when heterologously expressed in Escherichia coli. We use cryogenic electron microscopy to determine how RcpA and TadD assemble a secretin channel with C13 and C14 symmetries. Despite low sequence homology, we show that TadD shares a similar fold to the type 4 pilus system pilotin PilF. We establish that the C-terminal four residues of RcpA bind TadD - an interaction essential for secretin formation. The binding mechanism between RcpA and TadD appears distinct from known secretin-pilotin pairings in other secretion systems.
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Affiliation(s)
- Matteo Tassinari
- Department of Infectious Disease, Imperial College, London, SW7 2AZ, UK
- Human Technopole, Milan, Italy
| | - Marta Rudzite
- Department of Life Sciences, Imperial College, London, SW7 2AZ, UK
| | - Alain Filloux
- Department of Life Sciences, Imperial College, London, SW7 2AZ, UK
- Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, Singapore, Singapore
| | - Harry H Low
- Department of Infectious Disease, Imperial College, London, SW7 2AZ, UK.
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9
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Kumar S, Konovalova A. BamE directly interacts with BamA and BamD coordinating their functions. Mol Microbiol 2023; 120:397-407. [PMID: 37455652 PMCID: PMC10528117 DOI: 10.1111/mmi.15127] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2023] [Revised: 07/04/2023] [Accepted: 07/05/2023] [Indexed: 07/18/2023]
Abstract
The β-barrel assembly machinery (Bam) complex facilitates the assembly of outer membrane proteins (OMPs) in gram-negative bacteria. The Bam complex is conserved and essential for bacterial viability and consists of five subunits, BamA-E. BamA is the transmembrane component, and its β-barrel domain opens laterally to allow folding and insertion of incoming OMPs. The remaining components are regulatory, among which only BamD is essential. Previous studies suggested that BamB regulates BamA directly, while BamE and BamC serve as BamD regulators. However, specific molecular details of their functions remain unknown. Our previous research demonstrated that BamE plays a specialized role in assembling the complex between the lipoprotein RcsF and its OMP partners, required for the Regulator of Capsule Synthesis (Rcs) stress response. Here, we used RcsF/OmpA as a model substrate to investigate BamE function. Our results challenge the current view that BamE only serves as a BamD regulator. We show that BamE also directly interacts with BamA. BamE interaction with both BamA and BamD is important for function. Our genetic and biochemical analysis shows that BamE stabilizes the Bam complex and promotes bidirectional signaling interaction between BamA and BamD. This BamE function becomes essential when direct BamA/BamD communication is impeded.
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Affiliation(s)
- Santosh Kumar
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center at Houston (UTHealth), Houston, TX, 77030, USA
| | - Anna Konovalova
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center at Houston (UTHealth), Houston, TX, 77030, USA
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10
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Smithers L, Olatunji S, Caffrey M. Bacterial Lipoprotein Posttranslational Modifications. New Insights and Opportunities for Antibiotic and Vaccine Development. Front Microbiol 2021; 12:788445. [PMID: 34950121 PMCID: PMC8689077 DOI: 10.3389/fmicb.2021.788445] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2021] [Accepted: 11/16/2021] [Indexed: 12/17/2022] Open
Abstract
Lipoproteins are some of the most abundant proteins in bacteria. With a lipid anchor to the cell membrane, they function as enzymes, inhibitors, transporters, structural proteins, and as virulence factors. Lipoproteins activate the innate immune system and have biotechnological applications. The first lipoprotein was described by Braun and Rehn in 1969. Up until recently, however, work on lipoproteins has been sluggish, in part due to the challenges of handling proteins that are anchored to membranes by covalently linked lipids or are membrane integral. Activity in the area has quickened of late. In the past 5 years, high-resolution structures of the membrane enzymes of the canonical lipoprotein synthesis pathway have been determined, new lipoprotein types have been discovered and the enzymes responsible for their synthesis have been characterized biochemically. This has led to a flurry of activity aimed at developing novel antibiotics targeting these enzymes. In addition, surface exposed bacterial lipoproteins have been utilized as candidate vaccine antigens, and their potential to act as self-adjuvanting antigens is increasingly recognized. A summary of the latest developments in lipoproteins and their synthesis, as well as how this information is being exploited for therapeutic purposes is presented here.
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Affiliation(s)
- Luke Smithers
- School of Medicine, Trinity College Dublin, Dublin, Ireland
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
| | - Samir Olatunji
- School of Medicine, Trinity College Dublin, Dublin, Ireland
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
| | - Martin Caffrey
- School of Medicine, Trinity College Dublin, Dublin, Ireland
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
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11
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High-throughput suppressor screen demonstrates that RcsF monitors outer membrane integrity and not Bam complex function. Proc Natl Acad Sci U S A 2021; 118:2100369118. [PMID: 34349021 DOI: 10.1073/pnas.2100369118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The regulator of capsule synthesis (Rcs) is a complex signaling cascade that monitors gram-negative cell envelope integrity. The outer membrane (OM) lipoprotein RcsF is the sensory component, but how RcsF functions remains elusive. RcsF interacts with the β-barrel assembly machinery (Bam) complex, which assembles RcsF in complex with OM proteins (OMPs), resulting in RcsF's partial cell surface exposure. Elucidating whether RcsF/Bam or RcsF/OMP interactions are important for its sensing function is challenging because the Bam complex is essential, and partial loss-of-function mutations broadly compromise the OM biogenesis. Our recent discovery that, in the absence of nonessential component BamE, RcsF inhibits function of the central component BamA provided a genetic tool to select mutations that specifically prevent RcsF/BamA interactions. We employed a high-throughput suppressor screen to isolate a collection of such rcsF and bamA mutants and characterized their impact on RcsF/OMP assembly and Rcs signaling. Using these mutants and BamA inhibitors MRL-494L and darobactin, we provide multiple lines of evidence against the model in which RcsF senses Bam complex function. We show that Rcs activation in bam mutants results from secondary OM and lipopolysaccharide defects and that RcsF/OMP assembly is required for this activation, supporting an active role of RcsF/OMP complexes in sensing OM stress.
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12
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Steenhuis M, van Ulsen P, Martin NI, Luirink J. A ban on BAM: an update on inhibitors of the β-barrel assembly machinery. FEMS Microbiol Lett 2021; 368:6287571. [PMID: 34048543 DOI: 10.1093/femsle/fnab059] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Accepted: 05/26/2021] [Indexed: 12/15/2022] Open
Abstract
Gram-negative pathogens are a rapidly increasing threat to human health worldwide due to high rates of antibiotic resistance and the lack of development of novel antibiotics. The protective cell envelope of gram-negative bacteria is a major permeability barrier that contributes to the problem by restricting the uptake of antibiotics. On the other hand, its unique architecture also makes it a suitable target for antibiotic interference. In particular, essential multiprotein machines that are required for biogenesis of the outer membrane have attracted attention in antibacterial design strategies. Recently, significant progress has been made in the development of inhibitors of the β-barrel assembly machine (BAM) complex. Here, we summarize the current state of drug development efforts targeting the BAM complex in pursuit of new antibiotics.
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Affiliation(s)
- Maurice Steenhuis
- Department of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Vrije Universiteit, De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands
| | - Peter van Ulsen
- Department of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Vrije Universiteit, De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands
| | - Nathaniel I Martin
- Biological Chemistry Group, Institute of Biology Leiden, Leiden University, Nonnensteeg 3, 2311 VJ, Leiden, The Netherlands
| | - Joen Luirink
- Department of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Vrije Universiteit, De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands
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13
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Legood S, Boneca IG, Buddelmeijer N. Mode of action of lipoprotein modification enzymes-Novel antibacterial targets. Mol Microbiol 2021; 115:356-365. [PMID: 32979868 PMCID: PMC8048626 DOI: 10.1111/mmi.14610] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 09/10/2020] [Indexed: 01/04/2023]
Abstract
Lipoproteins are characterized by a fatty acid moiety at their amino-terminus through which they are anchored into membranes. They fulfill a variety of essential functions in bacterial cells, such as cell wall maintenance, virulence, efflux of toxic elements including antibiotics, and uptake of nutrients. The posttranslational modification process of lipoproteins involves the sequential action of integral membrane enzymes and phospholipids as acyl donors. In recent years, the structures of the lipoprotein modification enzymes have been solved by X-ray crystallography leading to a greater insight into their function and the molecular mechanism of the reactions. The catalytic domains of the enzymes are exposed to the periplasm or external milieu and are readily accessible to small molecules. Since the lipoprotein modification pathway is essential in proteobacteria, it is a potential target for the development of novel antibiotics. In this review, we discuss recent literature on the structural characterization of the enzymes, and the in vitro activity assays compatible with high-throughput screening for inhibitors, with perspectives on the development of new antimicrobial agents.
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Affiliation(s)
- Simon Legood
- Institut PasteurUnité Biologie et Génétique de la Paroi BactérienneParisFrance
- CNRS, UMR 2001 « Microbiologie intégrative et Moléculaire »ParisFrance
- INSERM Groupe AvenirParisFrance
- Université de ParisSorbonne Paris CitéParisFrance
| | - Ivo G. Boneca
- Institut PasteurUnité Biologie et Génétique de la Paroi BactérienneParisFrance
- CNRS, UMR 2001 « Microbiologie intégrative et Moléculaire »ParisFrance
- INSERM Groupe AvenirParisFrance
| | - Nienke Buddelmeijer
- Institut PasteurUnité Biologie et Génétique de la Paroi BactérienneParisFrance
- CNRS, UMR 2001 « Microbiologie intégrative et Moléculaire »ParisFrance
- INSERM Groupe AvenirParisFrance
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14
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Functions of the BamBCDE Lipoproteins Revealed by Bypass Mutations in BamA. J Bacteriol 2020; 202:JB.00401-20. [PMID: 32817097 DOI: 10.1128/jb.00401-20] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Accepted: 08/13/2020] [Indexed: 12/27/2022] Open
Abstract
The heteropentomeric β-barrel assembly machine (BAM complex) is responsible for folding and inserting a diverse array of β-barrel outer membrane proteins (OMPs) into the outer membrane (OM) of Gram-negative bacteria. The BAM complex contains two essential proteins, the β-barrel OMP BamA and a lipoprotein BamD, whereas the auxiliary lipoproteins BamBCE are individually nonessential. Here, we identify and characterize three bamA mutations, the E-to-K change at position 470 (bamAE470K ), the A-to-P change at position 496 (bamAA496P ), and the A-to-S change at position 499 (bamAA499S ), that suppress the otherwise lethal ΔbamD, ΔbamB ΔbamC ΔbamE, and ΔbamC ΔbamD ΔbamE mutations. The viability of cells lacking different combinations of BAM complex lipoproteins provides the opportunity to examine the role of the individual proteins in OMP assembly. Results show that, in wild-type cells, BamBCE share a redundant function; at least one of these lipoproteins must be present to allow BamD to coordinate productively with BamA. Besides BamA regulation, BamD shares an additional essential function that is redundant with a second function of BamB. Remarkably, bamAE470K suppresses both, allowing the construction of a BAM complex composed solely of BamAE470K that is able to assemble OMPs in the absence of BamBCDE. This work demonstrates that the BAM complex lipoproteins do not participate in the catalytic folding of OMP substrates but rather function to increase the efficiency of the assembly process by coordinating and regulating the assembly of diverse OMP substrates.IMPORTANCE The folding and insertion of β-barrel outer membrane proteins (OMPs) are conserved processes in mitochondria, chloroplasts, and Gram-negative bacteria. In Gram-negative bacteria, OMPs are assembled into the outer membrane (OM) by the heteropentomeric β-barrel assembly machine (BAM complex). In this study, we probe the function of the individual BAM proteins and how they coordinate assembly of a diverse family of OMPs. Furthermore, we identify a gain-of-function bamA mutant capable of assembling OMPs independently of all four other BAM proteins. This work advances our understanding of OMP assembly and sheds light on how this process is distinct in Gram-negative bacteria.
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The gain-of-function allele bamA E470K bypasses the essential requirement for BamD in β-barrel outer membrane protein assembly. Proc Natl Acad Sci U S A 2020; 117:18737-18743. [PMID: 32675245 DOI: 10.1073/pnas.2007696117] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The outer membrane (OM) of gram-negative bacteria confers innate resistance to toxins and antibiotics. Integral β-barrel outer membrane proteins (OMPs) function to establish and maintain the selective permeability of the OM. OMPs are assembled into the OM by the β-barrel assembly machine (BAM), which is composed of one OMP-BamA-and four lipoproteins-BamB, C, D, and E. BamB, C, and E can be removed individually with only minor effects on barrier function; however, depletion of either BamA or BamD causes a global defect in OMP assembly and results in cell death. We have identified a gain-of-function mutation, bamA E470K , that bypasses the requirement for BamD. Although bamD::kan bamA E470K cells exhibit growth and OM barrier defects, they assemble OMPs with surprising robustness. Our results demonstrate that BamD does not play a catalytic role in OMP assembly, but rather functions to regulate the activity of BamA.
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16
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Li Y, Zhu X, Zhang J, Lin Y, You X, Chen M, Wang Y, Zhu N, Si S. Identification of a Compound That Inhibits the Growth of Gram-Negative Bacteria by Blocking BamA-BamD Interaction. Front Microbiol 2020; 11:1252. [PMID: 32636816 PMCID: PMC7316895 DOI: 10.3389/fmicb.2020.01252] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 05/18/2020] [Indexed: 12/31/2022] Open
Abstract
The demand for novel antibiotics is imperative for drug-resistant Gram-negative bacteria which causes diverse intractable infection disease in clinic. Here, a comprehensive screening was implemented to identify potential agents that disrupt the assembly of β-barrel outer-membrane proteins (OMPs) in the outer membrane (OM) of Gram-negative bacteria. The assembly of OMPs requires ubiquitous β-barrel assembly machinery (BAM). Among the five protein subunits in BAM, the interaction between BamA and BamD is essential for the function of this complex. We first established a yeast two-hybrid (Y2H) system to confirm the interaction between BamA and BamD, and then screened agents that specifically disrupt this interaction. From this screen, we identified a compound IMB-H4 that specially blocks BamA–BamD interaction and selectively inhibits the growth of Escherichia coli and other Gram-negative bacteria. Moreover, our results suggest that IMB-H4 disrupts BamA–BamD interaction by binding to BamA. Strikingly, E. coli cells having been treated with IMB-H4 showed impaired OM integrity and decreased the abundance of OMPs. Therefore, an antibacterial agent was identified successfully using Y2H system, and this compound likely blocks the assembly of OMPs by targeting BamA–BamD interaction in Gram-negative bacteria.
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Affiliation(s)
- Yan Li
- Beijing Key Laboratory of Antimicrobial Agents, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Xiaohong Zhu
- Beijing Key Laboratory of Antimicrobial Agents, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Jing Zhang
- Beijing Key Laboratory of Antimicrobial Agents, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Yuan Lin
- Beijing Key Laboratory of Antimicrobial Agents, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.,State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences, Beijing, China
| | - Xuefu You
- Beijing Key Laboratory of Antimicrobial Agents, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Minghua Chen
- Beijing Key Laboratory of Antimicrobial Agents, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Yanchang Wang
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, United States
| | - Ningyu Zhu
- Beijing Key Laboratory of Antimicrobial Agents, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Shuyi Si
- Beijing Key Laboratory of Antimicrobial Agents, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
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Abstract
Spirochetes form a separate phylum of bacteria with two membranes but otherwise unusual morphologies and envelope structures. Distinctive common features of Borrelia, Leptospira, and Treponema include the sequestration of flagella to the periplasm and thin peptidoglycan cell walls that are more closely associated with the inner membrane. Outer membrane compositions differ significantly between the genera. Leptospira most closely track Gram-negative bacteria due to the incorporation of lipopolysaccharides. Treponema and Borrelia outer membranes lack lipopolysaccharide, with treponemes expressing only a few outer membrane proteins and Borrelia displaying a dizzying diversity of abundant surface lipoproteins instead. Phylogenetic and experimental evidence indicates that spirochetes have adapted various modules of bacterial export and secretion pathways to build and maintain their envelopes. Export and insertion pathways in the inner membrane appear conserved, while spirochetal experimentation with various envelope architectures over time has led to variations in secretion pathways in the periplasm and outer membrane. Classical type I to III secretion systems have been identified, with demonstrated roles in drug efflux and export of flagellar proteins only. Unique activities of periplasmic proteases, including a C-terminal protease, are involved in maturation of some periplasmic proteins. Proper lipoprotein sorting within the periplasm appears to be dependent on functional Lol pathways that lack the outer membrane lipoprotein insertase LolB. The abundance of surface lipoproteins in Borrelia and detailed protein sorting studies suggest a lipoprotein secretion pathway that either extends Lol through the outer membrane or bypasses it altogether. Proteins can be released from cells in outer membrane vesicles or, rarely, as soluble proteins.
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18
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Hews CL, Cho T, Rowley G, Raivio TL. Maintaining Integrity Under Stress: Envelope Stress Response Regulation of Pathogenesis in Gram-Negative Bacteria. Front Cell Infect Microbiol 2019; 9:313. [PMID: 31552196 PMCID: PMC6737893 DOI: 10.3389/fcimb.2019.00313] [Citation(s) in RCA: 77] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Accepted: 08/19/2019] [Indexed: 12/20/2022] Open
Abstract
The Gram-negative bacterial envelope is an essential interface between the intracellular and harsh extracellular environment. Envelope stress responses (ESRs) are crucial to the maintenance of this barrier and function to detect and respond to perturbations in the envelope, caused by environmental stresses. Pathogenic bacteria are exposed to an array of challenging and stressful conditions during their lifecycle and, in particular, during infection of a host. As such, maintenance of envelope homeostasis is essential to their ability to successfully cause infection. This review will discuss our current understanding of the σE- and Cpx-regulated ESRs, with a specific focus on their role in the virulence of a number of model pathogens.
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Affiliation(s)
- Claire L Hews
- School of Biological Sciences, University of East Anglia, Norwich, United Kingdom
| | - Timothy Cho
- Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
| | - Gary Rowley
- School of Biological Sciences, University of East Anglia, Norwich, United Kingdom
| | - Tracy L Raivio
- Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
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19
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Li Z, Wang Y, Li X, Lin Z, Lin Y, Srinivasan R, Lin X. The characteristics of antibiotic resistance and phenotypes in 29 outer‐membrane protein mutant strains inAeromonas hydrophila. Environ Microbiol 2019; 21:4614-4628. [DOI: 10.1111/1462-2920.14761] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2019] [Revised: 07/22/2019] [Accepted: 07/25/2019] [Indexed: 01/18/2023]
Affiliation(s)
- Zeqi Li
- Fujian Provincial Key Laboratory of Agroecological Processing and Safety Monitoring (School of Life Sciences)Fujian Agriculture and Forestry University) Fuzhou China
- Key Laboratory of Crop Ecology and Molecular Physiology (Fujian Agriculture and Forestry University)Fujian Province University Fuzhou China
| | - Yuqian Wang
- Fujian Provincial Key Laboratory of Agroecological Processing and Safety Monitoring (School of Life Sciences)Fujian Agriculture and Forestry University) Fuzhou China
- Key Laboratory of Crop Ecology and Molecular Physiology (Fujian Agriculture and Forestry University)Fujian Province University Fuzhou China
| | - Xiaoyan Li
- Fujian Provincial Key Laboratory of Agroecological Processing and Safety Monitoring (School of Life Sciences)Fujian Agriculture and Forestry University) Fuzhou China
- Key Laboratory of Crop Ecology and Molecular Physiology (Fujian Agriculture and Forestry University)Fujian Province University Fuzhou China
| | - Zhenping Lin
- Fujian Provincial Key Laboratory of Agroecological Processing and Safety Monitoring (School of Life Sciences)Fujian Agriculture and Forestry University) Fuzhou China
- Key Laboratory of Crop Ecology and Molecular Physiology (Fujian Agriculture and Forestry University)Fujian Province University Fuzhou China
| | - Yuexu Lin
- Fujian Provincial Key Laboratory of Agroecological Processing and Safety Monitoring (School of Life Sciences)Fujian Agriculture and Forestry University) Fuzhou China
- Key Laboratory of Crop Ecology and Molecular Physiology (Fujian Agriculture and Forestry University)Fujian Province University Fuzhou China
| | - Ramanathan Srinivasan
- Fujian Provincial Key Laboratory of Agroecological Processing and Safety Monitoring (School of Life Sciences)Fujian Agriculture and Forestry University) Fuzhou China
- Key Laboratory of Crop Ecology and Molecular Physiology (Fujian Agriculture and Forestry University)Fujian Province University Fuzhou China
| | - Xiangmin Lin
- Fujian Provincial Key Laboratory of Agroecological Processing and Safety Monitoring (School of Life Sciences)Fujian Agriculture and Forestry University) Fuzhou China
- Key Laboratory of Crop Ecology and Molecular Physiology (Fujian Agriculture and Forestry University)Fujian Province University Fuzhou China
- Key Laboratory of Marine Biotechnology of Fujian ProvinceInstitute of Oceanology, Fujian Agriculture and Forestry University Fuzhou 350002 China
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20
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Abstract
Lipoproteins are produced by both Gram-positive and Gram-negative bacteria. Once secreted, lipoproteins are quickly acylated, anchoring them into the plasma membrane. Recent work has shown that Gram-positive bacteria are able to generate considerable diversity in the acylation of their lipoproteins, though the mechanisms involved are only just beginning to emerge. In Gram-negative organisms, most lipoproteins are subsequently trafficked to the outer membrane (OM). Lipoprotein trafficking is an essential pathway in these bacteria. At least one OM lipoprotein component is required by each of the essential machines that assemble the OM (such as the Bam and Lpt machines) and build the peptidoglycan cell wall (Lpo-penicillin-binding protein complexes). The Lol pathway has been the paradigm for OM lipoprotein trafficking: a complex of LolCDE extracts lipoproteins from the plasma membrane, LolA shuttles them through the periplasmic space, and LolB anchors them into the OM. The peptide signals responsible for OM-targeting via LolCDE have long been known for Escherichia coli. Remarkably, production of novel lipoprotein acyl forms in E. coli has reinforced the idea that lipid signals also contribute to OM targeting via LolCDE. Moreover, recent work has shown that lipoprotein trafficking can occur in E. coli without either LolA or LolB. Therefore, current evidence suggests that at least one additional, LolAB-independent route for OM lipoprotein trafficking exists. This chapter reviews the posttranslocation modifications of all lipoproteins, with a focus on the trafficking of lipoproteins to the OM of Gram-negative bacteria.
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21
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Tata M, Konovalova A. Improper Coordination of BamA and BamD Results in Bam Complex Jamming by a Lipoprotein Substrate. mBio 2019; 10:e00660-19. [PMID: 31113900 PMCID: PMC6529637 DOI: 10.1128/mbio.00660-19] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Accepted: 04/16/2019] [Indexed: 12/13/2022] Open
Abstract
The β-barrel assembly machinery, the Bam complex, is central to the biogenesis of integral outer membrane proteins (OMPs) as well as OMP-dependent surface-exposed lipoproteins, such as regulator of capsule synthesis protein F (RcsF). Previous genetic analysis established the model that nonessential components BamE and BamB have overlapping, redundant functions to enhance the kinetics of the highly conserved BamA/BamD core. Here we report that BamE plays a specialized nonredundant role in the Bam complex required for surface exposure of RcsF. We show that the lack of bamE, but not bamB, completely abolishes assembly of RcsF/OMP complexes and establish that the inability to assemble RcsF/OMP complexes is a molecular reason underlying all synthetic lethal interactions of ΔbamE Our genetic analysis and biochemical cross-linking suggest that RcsF accumulates on BamA when BamA cannot engage with BamD because of its limited availability or the incompatible conformation. The role of BamE is to promote proper coordination of RcsF-bound BamA with BamD to complete OMP assembly around RcsF. We show that in the absence of BamE, RcsF is stalled on BamA, thus blocking its function, and we identify the lipoprotein RcsF as a bona fide jamming substrate of the Bam complex.IMPORTANCE The β-barrel assembly machinery, the Bam complex, consists of five components, BamA to -E, among which BamA and BamD are highly conserved and essential. The nonessential components are believed to play redundant roles simply by improving the rate of β-barrel folding. Here we show that BamE contributes a specific and nonoverlapping function to the Bam complex. BamE coordinates BamA and BamD to form a complex between the lipoprotein RcsF and its partner outer membrane β-barrel protein, allowing RcsF to reach the cell surface. In the absence of BamE, RcsF accumulates on BamA, thus blocking the activity of the Bam complex. As the Bam complex is a major antibiotic target in Gram-negative bacteria, the discovery that a lipoprotein can act as a jamming substrate may open the door for development of novel Bam complex inhibitors.
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Affiliation(s)
- Muralidhar Tata
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center at Houston (UTHealth), Houston, Texas, USA
| | - Anna Konovalova
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center at Houston (UTHealth), Houston, Texas, USA
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22
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Suppressor Mutations in degS Overcome the Acute Temperature-Sensitive Phenotype of Δ degP and Δ degP Δ tol-pal Mutants of Escherichia coli. J Bacteriol 2019; 201:JB.00742-18. [PMID: 30858298 DOI: 10.1128/jb.00742-18] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 02/25/2019] [Indexed: 11/20/2022] Open
Abstract
In Escherichia coli, the periplasmic protease DegP plays a critical role in degrading misfolded outer membrane proteins (OMPs). Consequently, mutants lacking DegP display a temperature-sensitive growth defect, presumably due to the toxic accumulation of misfolded OMPs. The Tol-Pal complex plays a poorly defined but an important role in envelope biogenesis, since mutants defective in this complex display a classical periplasmic leakage phenotype. Double mutants lacking DegP and an intact Tol-Pal complex display exaggerated temperature-sensitive growth defects and the leaky phenotype. Two revertants that overcome the temperature-sensitive growth phenotype carry missense mutations in the degS gene, resulting in D102V and D320A substitutions. D320 and E317 of the PDZ domain of DegS make salt bridges with R178 of DegS's protease domain to keep the protease in the inactive state. However, weakening of the tripartite interactions by D320A increases DegS's basal protease activity. Although the D102V substitution is as effective as D320A in suppressing the temperature-sensitive growth phenotype, the molecular mechanism behind its effect on DegS's protease activity is unclear. Our data suggest that the two DegS variants modestly activate RseA-controlled, σE-mediated envelope stress response pathway and elevate periplasmic protease activity to restore envelope homeostasis. Based on the release of a cytoplasmic enzyme in the culture supernatant, we conclude that the conditional lethal phenotype of ΔtolB ΔdegP mutants stems from a grossly destabilized envelope structure that causes excessive cell lysis. Together, the data point to a critical role for periplasmic proteases when the Tol-Pal complex-mediated envelope structure and/or functions are compromised.IMPORTANCE The Tol-Pal complex plays a poorly defined role in envelope biogenesis. The data presented here show that DegP's periplasmic protease activity becomes crucial in mutants lacking the intact Tol-Pal complex, but this requirement can be circumvented by suppressor mutations that activate the basal protease activity of a regulatory protease, DegS. These observations point to a critical role for periplasmic proteases when Tol-Pal-mediated envelope structure and/or functions are perturbed.
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23
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Ricci DP, Silhavy TJ. Outer Membrane Protein Insertion by the β-barrel Assembly Machine. EcoSal Plus 2019; 8:10.1128/ecosalplus.ESP-0035-2018. [PMID: 30869065 PMCID: PMC6419762 DOI: 10.1128/ecosalplus.esp-0035-2018] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
Abstract
Like all outer membrane (OM) constituents, integral OM β-barrel proteins in Gram-negative bacteria are synthesized in the cytoplasm and trafficked to the OM, where they are locally assembled into the growing OM by the ubiquitous β-barrel assembly machine (Bam). While the identities and structures of all essential and accessory Bam components have been determined, the basic mechanism of Bam-assisted OM protein integration remains elusive. Here we review mechanistic analyses of OM β-barrel protein folding and Bam dynamics and summarize recent insights that inform a general model for OM protein recognition and assembly by the Bam complex.
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Affiliation(s)
- Dante P Ricci
- Department of Early Research, Achaogen, Inc., South San Francisco, CA 94080
| | - Thomas J Silhavy
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544
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24
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Queiroz PS, Ruas FAD, Barboza NR, de Castro Borges W, Guerra-Sá R. Alterations in the proteomic composition of Serratia marcescens in response to manganese (II). BMC Biotechnol 2018; 18:83. [PMID: 30594179 PMCID: PMC6311052 DOI: 10.1186/s12896-018-0493-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2018] [Accepted: 12/17/2018] [Indexed: 02/03/2023] Open
Abstract
Background Proteomics is an important tool for the investigation of dynamic physiological responses of microbes under heavy metal stress. To gain insight into how bacteria respond to manganese (II) and identify the proteins involved in Mn (II) oxidation, the shotgun proteomics approach was applied to a potential Mn (II)-oxidizing Serratia marcescens strain cultivated in the absence and presence of Mn (II). Results The LG1 strain, which grew equally well in the two conditions, was found to express a set of proteins related to cellular processes vital for survival, as well as proteins involved in adaptation and tolerance to Mn (II). The multicopper oxidase CueO was identified, indicating its probable participation in the Mn (II) bio-oxidation; however, its expression was not modulated by the presence of Mn (II). A set of proteins related to cell and metabolic processes vital to the cells were downregulated in the presence of Mn (II), while cell membrane-related proteins involved in the maintenance of cell integrity and survival under stress were upregulated under this condition. Conclusions These findings indicate that the LG1 strain may be applied successfully in the bioremediation of Mn (II), and the shotgun approach provides an efficient means for obtaining the total proteome of this species.
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Affiliation(s)
- Pollyana Santos Queiroz
- Laboratório de Bioquímica e Biologia Molecular, Departamento de Ciências Biológicas (DECBI) & Instituto de Ciências Exatas e Biológica (NUPEB), Campus Morro do Cruzeiro, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil
| | - France Anne Dias Ruas
- Laboratório de Bioquímica e Biologia Molecular, Departamento de Ciências Biológicas (DECBI) & Instituto de Ciências Exatas e Biológica (NUPEB), Campus Morro do Cruzeiro, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil
| | - Natália Rocha Barboza
- Laboratório de Bioquímica e Biologia Molecular, Departamento de Ciências Biológicas (DECBI) & Instituto de Ciências Exatas e Biológica (NUPEB), Campus Morro do Cruzeiro, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil
| | - William de Castro Borges
- Laboratório de Enzimologia e Proteômica, Departamento de Ciências Biológicas (DECBI), Núcleo de Pesquisas em Ciências Biológicas, Universidade Federal de Ouro Preto, Ouro Preto, Minas Gerais, Brazil
| | - Renata Guerra-Sá
- Laboratório de Bioquímica e Biologia Molecular, Departamento de Ciências Biológicas (DECBI) & Instituto de Ciências Exatas e Biológica (NUPEB), Campus Morro do Cruzeiro, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil.
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25
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Houston S, Lithgow KV, Osbak KK, Kenyon CR, Cameron CE. Functional insights from proteome-wide structural modeling of Treponema pallidum subspecies pallidum, the causative agent of syphilis. BMC STRUCTURAL BIOLOGY 2018; 18:7. [PMID: 29769048 PMCID: PMC5956850 DOI: 10.1186/s12900-018-0086-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Accepted: 04/27/2018] [Indexed: 12/21/2022]
Abstract
Background Syphilis continues to be a major global health threat with 11 million new infections each year, and a global burden of 36 million cases. The causative agent of syphilis, Treponema pallidum subspecies pallidum, is a highly virulent bacterium, however the molecular mechanisms underlying T. pallidum pathogenesis remain to be definitively identified. This is due to the fact that T. pallidum is currently uncultivatable, inherently fragile and thus difficult to work with, and phylogenetically distinct with no conventional virulence factor homologs found in other pathogens. In fact, approximately 30% of its predicted protein-coding genes have no known orthologs or assigned functions. Here we employed a structural bioinformatics approach using Phyre2-based tertiary structure modeling to improve our understanding of T. pallidum protein function on a proteome-wide scale. Results Phyre2-based tertiary structure modeling generated high-confidence predictions for 80% of the T. pallidum proteome (780/978 predicted proteins). Tertiary structure modeling also inferred the same function as primary structure-based annotations from genome sequencing pipelines for 525/605 proteins (87%), which represents 54% (525/978) of all T. pallidum proteins. Of the 175 T. pallidum proteins modeled with high confidence that were not assigned functions in the previously annotated published proteome, 167 (95%) were able to be assigned predicted functions. Twenty-one of the 175 hypothetical proteins modeled with high confidence were also predicted to exhibit significant structural similarity with proteins experimentally confirmed to be required for virulence in other pathogens. Conclusions Phyre2-based structural modeling is a powerful bioinformatics tool that has provided insight into the potential structure and function of the majority of T. pallidum proteins and helped validate the primary structure-based annotation of more than 50% of all T. pallidum proteins with high confidence. This work represents the first T. pallidum proteome-wide structural modeling study and is one of few studies to apply this approach for the functional annotation of a whole proteome. Electronic supplementary material The online version of this article (10.1186/s12900-018-0086-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Simon Houston
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada
| | - Karen Vivien Lithgow
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada
| | | | - Chris Richard Kenyon
- HIV/STI Unit, Institute of Tropical Medicine, Antwerp, Belgium.,Division of Infectious Diseases and HIV Medicine, University of Cape Town, Cape Town, South Africa
| | - Caroline E Cameron
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada.
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26
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Abstract
The hallmark of gram-negative bacteria and organelles such as mitochondria and chloroplasts is the presence of an outer membrane. In bacteria such as Escherichia coli, the outer membrane is a unique asymmetric lipid bilayer with lipopolysaccharide in the outer leaflet. Integral transmembrane proteins assume a β-barrel structure, and their assembly is catalyzed by the heteropentameric Bam complex containing the outer membrane protein BamA and four lipoproteins, BamB-E. How the Bam complex assembles a great diversity of outer membrane proteins into a membrane without an obvious energy source is a particularly challenging problem, because folding intermediates are predicted to be unstable in either an aqueous or a hydrophobic environment. Two models have been put forward: the budding model, based largely on structural data, and the BamA assisted model, based on genetic and biochemical studies. Here we offer a critical discussion of the pros and cons of each.
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Affiliation(s)
- Anna Konovalova
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544;
| | - Daniel E Kahne
- Department of Chemistry and Chemical Biology and.,Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138.,Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115
| | - Thomas J Silhavy
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544;
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27
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Botos I, Noinaj N, Buchanan SK. Insertion of proteins and lipopolysaccharide into the bacterial outer membrane. Philos Trans R Soc Lond B Biol Sci 2018. [PMID: 28630161 DOI: 10.1098/rstb.2016.0224] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The bacterial outer membrane contains phospholipids in the inner leaflet and lipopolysaccharide (LPS) in the outer leaflet. Both proteins and LPS must be frequently inserted into the outer membrane to preserve its integrity. The protein complex that inserts LPS into the outer membrane is called LptDE, and consists of an integral membrane protein, LptD, with a separate globular lipoprotein, LptE, inserted in the barrel lumen. The protein complex that inserts newly synthesized outer-membrane proteins (OMPs) into the outer membrane is called the BAM complex, and consists of an integral membrane protein, BamA, plus four lipoproteins, BamB, C, D and E. Recent structural and functional analyses illustrate how these two complexes insert their substrates into the outer membrane by distorting the membrane component (BamA or LptD) to directly access the lipid bilayer.This article is part of the themed issue 'Membrane pores: from structure and assembly, to medicine and technology'.
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Affiliation(s)
- Istvan Botos
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Nicholas Noinaj
- Markey Center for Structural Biology, Department of Biological Sciences, and the Purdue Institute for Inflammation, Immunology and Infectious Diseases, Purdue University, West Lafayette, Indiana 47907, USA
| | - Susan K Buchanan
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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28
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Substrate binding to BamD triggers a conformational change in BamA to control membrane insertion. Proc Natl Acad Sci U S A 2018; 115:2359-2364. [PMID: 29463713 DOI: 10.1073/pnas.1711727115] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The β-barrel assembly machine (Bam) complex folds and inserts integral membrane proteins into the outer membrane of Gram-negative bacteria. The two essential components of the complex, BamA and BamD, both interact with substrates, but how the two coordinate with each other during assembly is not clear. To elucidate aspects of this process we slowed the assembly of an essential β-barrel substrate of the Bam complex, LptD, by changing a conserved residue near the C terminus. This defective substrate is recruited to the Bam complex via BamD but is unable to integrate into the membrane efficiently. Changes in the extracellular loops of BamA partially restore assembly kinetics, implying that BamA fails to engage this defective substrate. We conclude that substrate binding to BamD activates BamA by regulating extracellular loop interactions for folding and membrane integration.
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29
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Hsueh YC, Flinner N, Gross LE, Haarmann R, Mirus O, Sommer MS, Schleiff E. Chloroplast outer envelope protein P39 in Arabidopsis thaliana belongs to the Omp85 protein family. Proteins 2017; 85:1391-1401. [PMID: 25401771 DOI: 10.1002/prot.24725] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 10/14/2014] [Accepted: 11/03/2014] [Indexed: 01/08/2023]
Abstract
Proteins of the Omp85 family chaperone the membrane insertion of β-barrel-shaped outer membrane proteins in bacteria, mitochondria, and probably chloroplasts and facilitate the transfer of nuclear-encoded cytosolically synthesized preproteins across the outer envelope of chloroplasts. This protein family is characterized by N-terminal polypeptide transport-associated (POTRA) domains and a C-terminal membrane-embedded β-barrel. We have investigated a recently identified Omp85 family member of Arabidopsis thaliana annotated as P39. We show by in vitro and in vivo experiments that P39 is localized in chloroplasts. The electrophysiological properties of P39 are consistent with those of other Omp85 family members confirming the sequence based assignment of P39 to this family. Bioinformatic analysis showed that P39 lacks any POTRA domain, while a complete 16 stranded β-barrel including the highly conserved L6 loop is proposed. The electrophysiological properties are most comparable to Toc75-V, which is consistent with the phylogenetic clustering of P39 in the Toc75-V rather than the Toc75-III branch of the Omp85 family tree. Taken together P39 forms a pore with Omp85 family protein characteristics. The bioinformatic comparison of the pore region of Toc75-III, Toc75-V, and P39 shows distinctions of the barrel region most likely related to function. Proteins 2017; 85:1391-1401. © 2014 Wiley Periodicals, Inc.
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Affiliation(s)
- Yi-Ching Hsueh
- Department of Molecular Cell Biology of Plants, Goethe University, D-60438, Frankfurt, Germany
| | - Nadine Flinner
- Department of Molecular Cell Biology of Plants, Goethe University, D-60438, Frankfurt, Germany.,Center of Membrane Proteomics, Goethe University, D-60438, Frankfurt, Germany
| | - Lucia E Gross
- Department of Molecular Cell Biology of Plants, Goethe University, D-60438, Frankfurt, Germany
| | - Raimund Haarmann
- Department of Molecular Cell Biology of Plants, Goethe University, D-60438, Frankfurt, Germany
| | - Oliver Mirus
- Department of Molecular Cell Biology of Plants, Goethe University, D-60438, Frankfurt, Germany
| | - Maik S Sommer
- Department of Molecular Cell Biology of Plants, Goethe University, D-60438, Frankfurt, Germany
| | - Enrico Schleiff
- Department of Molecular Cell Biology of Plants, Goethe University, D-60438, Frankfurt, Germany.,Center of Membrane Proteomics, Goethe University, D-60438, Frankfurt, Germany.,Cluster of Excellence Frankfurt, Goethe University, D-60438, Frankfurt, Germany.,Buchman Institute of Molecular Life Sciences, Goethe University, D-60438, Frankfurt, Germany
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30
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Membrane integration of an essential β-barrel protein prerequires burial of an extracellular loop. Proc Natl Acad Sci U S A 2017; 114:2598-2603. [PMID: 28223520 DOI: 10.1073/pnas.1616576114] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The Bam complex assembles β-barrel proteins into the outer membrane (OM) of Gram-negative bacteria. These proteins comprise cylindrical β-sheets with long extracellular loops and create pores to allow passage of nutrients and waste products across the membrane. Despite their functional importance, several questions remain about how these proteins are assembled into the OM after their synthesis in the cytoplasm and secretion across the inner membrane. To understand this process better, we studied the assembly of an essential β-barrel substrate for the Bam complex, BamA. By mutating conserved residues in the β-barrel domain of this protein, we generated three assembly-defective BamA substrates that stall early in the folding process in the periplasm. Two of the three defective substrates, which harbor mutations within β-strands, fail to associate productively with the Bam complex. The third substrate, which harbors mutations in a conserved extracellular loop, accumulates on BamD during assembly, but does not integrate efficiently into the membrane. The assembly of all three substrates can be restored by artificially tethering a region of the substrate, which ultimately becomes an extracellular loop, to the lumen of the forming β-barrel. These results imply that a critical step in the folding process involves the interaction of residues on the interior of the nascent β-barrel wall with residues in one of the extracellular loops. We conclude that a prerequisite for membrane integration of β-barrel proteins is burial of the extracellular loops within the forming β-barrel.
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31
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Folding outer membrane proteins independently of the β-barrel assembly machinery: an assembly pathway for multimeric complexes? Biochem Soc Trans 2016; 44:845-50. [DOI: 10.1042/bst20160003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Indexed: 11/17/2022]
Abstract
Since the discovery of the essential role of the β-barrel assembly machinery (BAM) for the membrane insertion of outer membrane proteins (OMPs) that are unrelated in sequence, members of this universally conserved family dominate discussions on OMP assembly in bacteria, mitochondria and chloroplasts. However, several multimeric bacterial OMPs assemble independently of the catalyzing BAM-component BamA. Recent progress on this alternative pathway is reviewed here, and a model for BAM-independent assembly for multimeric OMPs is proposed in which monomer delivery to the membrane and stable prepore formation are key steps towards productive membrane insertion.
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32
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Broad W, Ling Q, Jarvis P. New Insights Into Roles of Ubiquitin Modification in Regulating Plastids and Other Endosymbiotic Organelles. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 325:1-33. [PMID: 27241217 DOI: 10.1016/bs.ircmb.2016.02.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Recent findings have revealed important and diverse roles for the ubiquitin modification of proteins in the regulation of endosymbiotic organelles, which include the primary plastids of plants as well as complex plastids: the secondary endosymbiotic organelles of cryptophytes, alveolates, stramenopiles, and haptophytes. Ubiquitin modifications have a variety of potential consequences, both to the modified protein itself and to cellular regulation. The ubiquitin-proteasome system (UPS) can target individual proteins for selective degradation by the cytosolic 26S proteasome. Ubiquitin modifications can also signal the removal of whole endosymbiotic organelles, for example, via autophagy as has been well characterized in mitochondria. As plastids must import over 90% of their proteins from the cytosol, the observation that the UPS selectively targets the plastid protein import machinery is particularly significant. In this way, the UPS may influence the development and interconversions of different plastid types, as well as plastid responses to stress, by reconfiguring the organellar proteome. In complex plastids, the Symbiont-derived ERAD-Like Machinery (SELMA) has coopted the protein transport capabilities of the ER-Associated Degradation (ERAD) system, whereby misfolded proteins are retrotranslocated from ER for proteasomal degradation, uncoupling them from proteolysis: SELMA components have been retargeted to the second outermost plastid membrane to mediate protein import. In spite of this wealth of new information, there still remain a large number of unanswered questions and a need to define the roles of ubiquitin modification further in the regulation of plastids.
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Affiliation(s)
- W Broad
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
| | - Q Ling
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
| | - P Jarvis
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom.
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33
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Gu Y, Li H, Dong H, Zeng Y, Zhang Z, Paterson NG, Stansfeld PJ, Wang Z, Zhang Y, Wang W, Dong C. Structural basis of outer membrane protein insertion by the BAM complex. Nature 2016; 531:64-9. [PMID: 26901871 DOI: 10.1038/nature17199] [Citation(s) in RCA: 205] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Accepted: 02/05/2016] [Indexed: 02/06/2023]
Abstract
All Gram-negative bacteria, mitochondria and chloroplasts have outer membrane proteins (OMPs) that perform many fundamental biological processes. The OMPs in Gram-negative bacteria are inserted and folded into the outer membrane by the β-barrel assembly machinery (BAM). The mechanism involved is poorly understood, owing to the absence of a structure of the entire BAM complex. Here we report two crystal structures of the Escherichia coli BAM complex in two distinct states: an inward-open state and a lateral-open state. Our structures reveal that the five polypeptide transport-associated domains of BamA form a ring architecture with four associated lipoproteins, BamB-BamE, in the periplasm. Our structural, functional studies and molecular dynamics simulations indicate that these subunits rotate with respect to the integral membrane β-barrel of BamA to induce movement of the β-strands of the barrel and promote insertion of the nascent OMP.
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Affiliation(s)
- Yinghong Gu
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
| | - Huanyu Li
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
| | - Haohao Dong
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
| | - Yi Zeng
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
| | - Zhengyu Zhang
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
| | - Neil G Paterson
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK
| | - Phillip J Stansfeld
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Zhongshan Wang
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.,Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical College, Xuzhou 221004, China.,Key Laboratory of Bio-resources and Eco-environment, Ministry of Education, Sichuan Key Laboratory of Molecular Biology and Biotechnology, College of Life Sciences, Sichuan University, Chengdu 610064, China
| | - Yizheng Zhang
- Key Laboratory of Bio-resources and Eco-environment, Ministry of Education, Sichuan Key Laboratory of Molecular Biology and Biotechnology, College of Life Sciences, Sichuan University, Chengdu 610064, China
| | - Wenjian Wang
- Laboratory of Department of Surgery, the First Affiliated Hospital, Sun Yat-sen University, 58 Zhongshan Road II, Guangzhou, Guangdong 510080, China
| | - Changjiang Dong
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
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34
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Chen Z, Zhan LH, Hou HF, Gao ZQ, Xu JH, Dong C, Dong YH. Structural basis for the interaction of BamB with the POTRA3-4 domains of BamA. ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY 2016; 72:236-44. [PMID: 26894671 DOI: 10.1107/s2059798315024729] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Accepted: 12/23/2015] [Indexed: 11/10/2022]
Abstract
In Escherichia coli, the Omp85 protein BamA and four lipoproteins (BamBCDE) constitute the BAM complex, which is essential for the assembly and insertion of outer membrane proteins into the outer membrane. Here, the crystal structure of BamB in complex with the POTRA3-4 domains of BamA is reported at 2.1 Å resolution. Based on this structure, the POTRA3 domain is associated with BamB via hydrogen-bonding and hydrophobic interactions. Structural and biochemical analysis revealed that the conserved residues Arg77, Glu127, Glu150, Ser167, Leu192, Leu194 and Arg195 of BamB play an essential role in interaction with the POTRA3 domain.
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Affiliation(s)
- Zhen Chen
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Li Hong Zhan
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Hai Feng Hou
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Zeng Qiang Gao
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Jian Hua Xu
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Cheng Dong
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Yu Hui Dong
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China
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35
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Kleanthous C, Rassam P, Baumann CG. Protein-protein interactions and the spatiotemporal dynamics of bacterial outer membrane proteins. Curr Opin Struct Biol 2015; 35:109-15. [PMID: 26629934 PMCID: PMC4684144 DOI: 10.1016/j.sbi.2015.10.007] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Revised: 10/26/2015] [Accepted: 10/30/2015] [Indexed: 01/14/2023]
Abstract
We discuss spatiotemporal patterning in the bacterial outer membrane. Promiscuous interactions between outer membrane proteins govern their behaviour. Turnover and biogenesis of outer membrane proteins linked to formation of clusters. Implications of spatiotemporal patterning for bacterial physiology discussed.
It has until recently been unclear whether outer membrane proteins (OMPs) of Gram-negative bacteria are organized or distributed randomly. Studies now suggest promiscuous protein–protein interactions (PPIs) between β-barrel OMPs in Escherichia coli govern their local and global dynamics, engender spatiotemporal patterning of the outer membrane into micro-domains and are the basis of β-barrel protein turnover. We contextualize these latest advances, speculate on areas of bacterial cell biology that might be influenced by the organization of OMPs into supramolecular assemblies, and highlight the new questions and controversies this revised view of the bacterial outer membrane raises.
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Affiliation(s)
- Colin Kleanthous
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
| | - Patrice Rassam
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
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36
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Noinaj N, Rollauer SE, Buchanan SK. The β-barrel membrane protein insertase machinery from Gram-negative bacteria. Curr Opin Struct Biol 2015; 31:35-42. [PMID: 25796031 PMCID: PMC4476940 DOI: 10.1016/j.sbi.2015.02.012] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 02/06/2015] [Accepted: 02/23/2015] [Indexed: 12/25/2022]
Abstract
The outer membranes (OM) of Gram-negative bacteria contain a host of β-barrel outer membrane proteins (OMPs) which serve many functions for cell survival and virulence. The biogenesis of these OMPs is mediated by the β-barrel assembly machinery (BAM) complex which is composed of five components including the essential core component called BamA that mediates the insertase function within the OM. The crystal structure of BamA has recently been reported from three different species, including a full-length structure from Neisseria gonorrhoeae. Mutagenesis and functional studies identified several conformational changes within BamA that are required for function, providing a significant advancement towards unraveling exactly how BamA and the BAM complex are able to fold and insert new OMPs in the OM.
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Affiliation(s)
- Nicholas Noinaj
- Markey Center for Structural Biology, Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, United States
| | - Sarah E Rollauer
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, United States
| | - Susan K Buchanan
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, United States.
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37
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Dunn JP, Kenedy MR, Iqbal H, Akins DR. Characterization of the β-barrel assembly machine accessory lipoproteins from Borrelia burgdorferi. BMC Microbiol 2015; 15:70. [PMID: 25887384 PMCID: PMC4377024 DOI: 10.1186/s12866-015-0411-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Accepted: 03/12/2015] [Indexed: 12/26/2022] Open
Abstract
Background Like all diderm bacteria studied to date, Borrelia burgdorferi possesses a β-barrel assembly machine (BAM) complex. The bacterial BAM complexes characterized thus far consist of an essential integral outer membrane protein designated BamA and one or more accessory proteins. The accessory proteins are typically lipid-modified proteins anchored to the inner leaflet of the outer membrane through their lipid moieties. We previously identified and characterized the B. burgdorferi BamA protein in detail and more recently identified two lipoproteins encoded by open reading frames bb0324 and bb0028 that associate with the borrelial BamA protein. The role(s) of the BAM accessory lipoproteins in B. burgdorferi is currently unknown. Results Structural modeling of B. burgdorferi BB0028 revealed a distinct β-propeller fold similar to the known structure for the E. coli BAM accessory lipoprotein BamB. Additionally, the structural model for BB0324 was highly similar to the known structure of BamD, which is consistent with the prior finding that BB0324 contains tetratricopeptide repeat regions similar to other BamD orthologs. Consistent with BB0028 and BB0324 being BAM accessory lipoproteins, mutants lacking expression of each protein were found to exhibit altered membrane permeability and enhanced sensitivity to various antimicrobials. Additionally, BB0028 mutants also exhibited significantly impaired in vitro growth. Finally, immunoprecipitation experiments revealed that BB0028 and BB0324 each interact specifically and independently with BamA to form the BAM complex in B. burgdorferi. Conclusions Combined structural studies, functional assays, and co-immunoprecipitation experiments confirmed that BB0028 and BB0324 are the respective BamB and BamD orthologs in B. burgdorferi, and are important in membrane integrity and/or outer membrane protein localization. The borrelial BamB and BamD proteins both interact specifically and independently with BamA to form a tripartite BAM complex in B. burgdorferi. A working model has been developed to further analyze outer membrane biogenesis and outer membrane protein transport in this pathogenic spirochete.
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Affiliation(s)
- Joshua P Dunn
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA.
| | - Melisha R Kenedy
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA.
| | - Henna Iqbal
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA.
| | - Darrin R Akins
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA.
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38
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Editorial Overview: Elucidation of Protein Translocation Pathways, Part I. J Mol Biol 2015; 427:997-8. [DOI: 10.1016/j.jmb.2015.01.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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39
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Ricci DP. Construction and Characterization of an E. coli bamD Depletion Strain. Methods Mol Biol 2015; 1329:227-243. [PMID: 26427689 DOI: 10.1007/978-1-4939-2871-2_18] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The central Bam components BamA and BamD are both essential genes in E. coli, a fact that often confounds genetic analysis using classical methods. The isolation of "depletion strains" in which these genes can be conditionally expressed removes this obstacle and facilitates the in vivo characterization of Bam function. This chapter describes an efficient two-step recombineering method for the construction of such a depletion strain, which contains an arabinose-inducible allele of bamD, using the λ Red system. Additionally, a simple protocol is presented for the depletion of bamD expression in live cells, which is particularly useful for the characterization of mutant alleles of bamD (complementation analysis). In principle, the procedures described can be adapted to produce and characterize depletion strains for any essential gene in E. coli or any other bacterium that is similarly amenable to genome engineering.
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Affiliation(s)
- Dante P Ricci
- Department of Developmental Biology, Stanford University School of Medicine, 279 Campus Drive West, Beckman Center, Stanford, CA, 94305, USA.
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