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Abstract
Bacterial type IV secretion systems (T4SSs) are a versatile group of nanomachines that can horizontally transfer DNA through conjugation and deliver effector proteins into a wide range of target cells. The components of T4SSs in gram-negative bacteria are organized into several large subassemblies: an inner membrane complex, an outer membrane core complex, and, in some species, an extracellular pilus. Cryo-electron tomography has been used to define the structures of T4SSs in intact bacteria, and high-resolution structural models are now available for isolated core complexes from conjugation systems, the Xanthomonas citri T4SS, the Helicobacter pylori Cag T4SS, and the Legionella pneumophila Dot/Icm T4SS. In this review, we compare the molecular architectures of these T4SSs, focusing especially on the structures of core complexes. We discuss structural features that are shared by multiple T4SSs as well as evolutionary strategies used for T4SS diversification. Finally, we discuss how structural variations among T4SSs may confer specialized functional properties.
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Affiliation(s)
- Michael J. Sheedlo
- Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Melanie D. Ohi
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America
| | - D. Borden Lacy
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America
- Veterans Affairs Tennessee Valley Healthcare System, Nashville, Tennessee, United States of America
| | - Timothy L. Cover
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America
- Veterans Affairs Tennessee Valley Healthcare System, Nashville, Tennessee, United States of America
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America
- * E-mail:
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VirB4- and VirD4-Like ATPases, Components of a Putative Type 4C Secretion System in Clostridioides difficile. J Bacteriol 2021; 203:e0035921. [PMID: 34424036 DOI: 10.1128/jb.00359-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The type 4 secretion system (T4SS) represents a bacterial nanomachine capable of trans-cell wall transportation of proteins and DNA and has attracted intense interest due to its roles in the pathogenesis of infectious diseases. In the current investigation, we uncovered three distinct gene clusters in Clostridioides difficile strain 630 encoding proteins structurally related to components of the VirB4/D4 type 4C secretion system from Streptococcus suis strain 05ZYH33 and located within sequences of conjugative transposons (CTn). Phylogenic analysis revealed that VirB4- and VirD4-like proteins of the CTn4 locus, on the one hand, and those of the CTn2 and CTn5 loci, on the other hand, fit into separate clades, suggesting specific roles of identified secretion system variants in the physiology of C. difficile. Our further study on VirB4- and VirD4-like products encoded by CTn4 revealed that both proteins possess Mg2+-dependent ATPase activity, form oligomers (most likely hexamers) in aqueous solutions, and rely on potassium but not sodium ions for the highest catalytic rate. VirD4 binds nonspecifically to DNA and RNA. The DNA-binding activity of VirD4 strongly decreased with the W241A variant. Mutations in the nucleotide sequences encoding presumable Walker A and Walker B motifs decreased the stability of the oligomers and significantly but not completely attenuated the enzymatic activity of VirB4. In VirD4, substitutions of amino acid residues in the peptides reminiscent of Walker structural motifs neither attenuated the enzymatic activity of the protein nor influenced the oligomerization state of the ATPase. IMPORTANCE C. difficile is a Gram-positive, anaerobic, spore-forming bacterium that causes life-threatening colitis in humans. Major virulence factors of the microorganism include the toxins TcdA, TcdB, and CDT. However, other bacterial products, including a type 4C secretion system, have been hypothesized to contribute to the pathogenesis of the infection and are considered possible virulence factors of C. difficile. In the current paper, we describe the structural organization of putative T4SS machinery in C. difficile and characterize its VirB4- and VirD4-like components. Our studies, in addition to its significance for basic science, can potentially aid the development of antivirulence drugs suitable for the treatment of C. difficile infection.
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Grohmann E, Christie PJ, Waksman G, Backert S. Type IV secretion in Gram-negative and Gram-positive bacteria. Mol Microbiol 2018; 107:455-471. [PMID: 29235173 PMCID: PMC5796862 DOI: 10.1111/mmi.13896] [Citation(s) in RCA: 222] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 12/07/2017] [Accepted: 12/09/2017] [Indexed: 02/06/2023]
Abstract
Type IV secretion systems (T4SSs) are versatile multiprotein nanomachines spanning the entire cell envelope in Gram-negative and Gram-positive bacteria. They play important roles through the contact-dependent secretion of effector molecules into eukaryotic hosts and conjugative transfer of mobile DNA elements as well as contact-independent exchange of DNA with the extracellular milieu. In the last few years, many details on the molecular mechanisms of T4SSs have been elucidated. Exciting structures of T4SS complexes from Escherichia coli plasmids R388 and pKM101, Helicobacter pylori and Legionella pneumophila have been solved. The structure of the F-pilus was also reported and surprisingly revealed a filament composed of pilin subunits in 1:1 stoichiometry with phospholipid molecules. Many new T4SSs have been identified and characterized, underscoring the structural and functional diversity of this secretion superfamily. Complex regulatory circuits also have been shown to control T4SS machine production in response to host cell physiological status or a quorum of bacterial recipient cells in the vicinity. Here, we summarize recent advances in our knowledge of 'paradigmatic' and emerging systems, and further explore how new basic insights are aiding in the design of strategies aimed at suppressing T4SS functions in bacterial infections and spread of antimicrobial resistances.
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Affiliation(s)
- Elisabeth Grohmann
- Beuth University of Applied Sciences Berlin, Life Sciences and Technology, D-13347 Berlin, Germany
| | - Peter J. Christie
- Department of Microbiology and Molecular Genetics, The University of Texas Medical School at Houston, 6431 Fannin St, Houston, Texas 77030, USA
| | - Gabriel Waksman
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, London WC1E 7HX, United Kingdom
| | - Steffen Backert
- Friedrich Alexander University Erlangen-Nuremberg, Department of Biology, Division of Microbiology, Staudtstrasse 5, D-91058 Erlangen, Germany
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Shrivastav A, Dabrowski AN, Conrad C, Baal N, Hackstein H, Plog S, Dietert K, Gruber AD, N'Guessan PD, Aly S, Suttorp N, Zahlten J. Peptidoglycan Recognition Protein 3 Does Not Alter the Outcome of Pneumococcal Pneumonia in Mice. Front Microbiol 2018; 9:103. [PMID: 29449834 PMCID: PMC5799233 DOI: 10.3389/fmicb.2018.00103] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 01/17/2018] [Indexed: 01/07/2023] Open
Abstract
Pneumococci frequently cause community-acquired pneumonia, a disease with high mortality rates, particularly in young children and in the elderly. Endogenous antimicrobial peptides and proteins such as PGLYRP3 may contribute to the progression and outcome of this disease. Since increasing antibiotic resistant strains occur all over the world, these endogenous antimicrobial molecules are interesting new targets for future therapies. In this study, the expression pattern of PGLYRP3 was analyzed in alveolar epithelial cells, alveolar macrophages and neutrophils. Additionally, the function of PGLYRP3 during Streptococcus pneumoniae-induced pneumonia was investigated in a murine pneumococcal pneumonia model using PGLYRP3KO mice. PGLYRP3 is expressed in all selected cell types but pneumococcus-dependent induction of PGLYRP3 was observed only in neutrophils and alveolar macrophages. Interestingly, there were no significant differences in the bacterial loads within the lungs, the blood or the spleens, in the cytokine response, the composition of immune cells and the histopathology between wild type and PGLYRP3KO mice. Finally, we could neither observe significant differences in the clinical symptoms nor in the overall survival. Collectively, PGLYRP3 seems to be dispensable for the antibacterial defense during pneumococcal pneumonia.
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Affiliation(s)
- Anshu Shrivastav
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Alexander N Dabrowski
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Claudia Conrad
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Nelli Baal
- Institute for Clinical Immunology and Transfusion Medicine, Justus-Liebig-Universität Giessen, Giessen, Germany
| | - Holger Hackstein
- Institute for Clinical Immunology and Transfusion Medicine, Justus-Liebig-Universität Giessen, Giessen, Germany
| | - Stephanie Plog
- Department of Veterinary Pathology, Freie Universität Berlin, Berlin, Germany
| | - Kristina Dietert
- Department of Veterinary Pathology, Freie Universität Berlin, Berlin, Germany
| | - Achim D Gruber
- Department of Veterinary Pathology, Freie Universität Berlin, Berlin, Germany
| | - Philippe D N'Guessan
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Sahar Aly
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Norbert Suttorp
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Janine Zahlten
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité - Universitätsmedizin Berlin, Berlin, Germany
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Grohmann E, Keller W, Muth G. Mechanisms of Conjugative Transfer and Type IV Secretion-Mediated Effector Transport in Gram-Positive Bacteria. Curr Top Microbiol Immunol 2017. [PMID: 29536357 DOI: 10.1007/978-3-319-75241-9_5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Conjugative DNA transfer is the most important means to transfer antibiotic resistance genes and virulence determinants encoded by plasmids, integrative conjugative elements (ICE), and pathogenicity islands among bacteria. In gram-positive bacteria, there exist two types of conjugative systems, (i) type IV secretion system (T4SS)-dependent ones, like those encoded by the Enterococcus, Streptococcus, Staphylococcus, Bacillus, and Clostridia mobile genetic elements and (ii) T4SS-independent ones, as those found on Streptomyces plasmids. Interestingly, very recently, on the Streptococcus suis genome, the first gram-positive T4SS not only involved in conjugative DNA transfer but also in effector translocation to the host was detected. Although no T4SS core complex structure from gram-positive bacteria is available, several structures from T4SS protein key factors from Enterococcus and Clostridia plasmids have been solved. In this chapter, we summarize the current knowledge on the molecular mechanisms and structure-function relationships of the diverse conjugation machineries and emerging research needs focused on combatting infections and spread of multiple resistant gram-positive pathogens.
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Affiliation(s)
- Elisabeth Grohmann
- Beuth University of Applied Sciences Berlin, Life Sciences and Technology, 13347, Berlin, Germany.
| | - Walter Keller
- Institute of Molecular Biosciences, BioTechMed, University of Graz, 8010, Graz, Austria
| | - Günther Muth
- Interfaculty Institute of Microbiology and Infection Medicine Tübingen, University Tübingen, 72076, Tübingen, Germany
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