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Monaci V, Gasperini G, Banci L, Micoli F, Cantini F. 1H, 13C and 15N assignment of self-complemented MrkA protein antigen from Klebsiella pneumoniae. BIOMOLECULAR NMR ASSIGNMENTS 2024:10.1007/s12104-024-10185-3. [PMID: 39018011 DOI: 10.1007/s12104-024-10185-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2024] [Accepted: 06/17/2024] [Indexed: 07/18/2024]
Abstract
Klebsiella pneumoniae (Kp) poses an escalating threat to public health, particularly given its association with nosocomial infections and its emergence as a leading cause of neonatal sepsis, particularly in low- and middle-income countries (LMICs). Host cell adherence and biofilm formation of Kp is mediated by type 1 and type 3 fimbriae whose major fimbrial subunits are encoded by the fimA and mrkA genes, respectively. In this study, we focus on MrkA subunit, which is a 20 KDa protein whose 3D molecular structure remains elusive. We applied solution NMR to characterize a recombinant version of MrkA in which the donor strand segment situated at the protein's N-terminus is relocated to the C-terminus, preceded by a hexaglycine linker. This construct yields a self-complemented variant of MrkA. Remarkably, the self-complemented MrkA monomer loses its capacity to interact with other monomers and to extend into fimbriae structures. Here, we report the nearly complete assignment of the 13C,15N labelled self-complemented MrkA monomer. Furthermore, an examination of its internal mobility unveiled that relaxation parameters are predominantly uniform across the polypeptide sequence, except for the glycine-rich region within loop 176-181. These data pave the way to a comprehensive structural elucidation of the MrkA monomer and to structurally map the molecular interaction regions between MrkA and antigen-induced antibodies.
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Affiliation(s)
- Valentina Monaci
- Magnetic Resonance Center - CERM, University of Florence, Via Luigi Sacconi 6, Sesto Fiorentino, 50019, Florence, Italy
- Department of Chemistry, University of Florence, Via della Lastruccia 3, Sesto Fiorentino, 50019, Florence, Italy
- GSK Vaccines Institute for Global Health (GVGH), Via Fiorentina 1, 53100, Siena, Italy
| | | | - Lucia Banci
- Magnetic Resonance Center - CERM, University of Florence, Via Luigi Sacconi 6, Sesto Fiorentino, 50019, Florence, Italy
- Department of Chemistry, University of Florence, Via della Lastruccia 3, Sesto Fiorentino, 50019, Florence, Italy
| | - Francesca Micoli
- GSK Vaccines Institute for Global Health (GVGH), Via Fiorentina 1, 53100, Siena, Italy
| | - Francesca Cantini
- Magnetic Resonance Center - CERM, University of Florence, Via Luigi Sacconi 6, Sesto Fiorentino, 50019, Florence, Italy.
- Department of Chemistry, University of Florence, Via della Lastruccia 3, Sesto Fiorentino, 50019, Florence, Italy.
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Arato V, Raso MM, Gasperini G, Berlanda Scorza F, Micoli F. Prophylaxis and Treatment against Klebsiella pneumoniae: Current Insights on This Emerging Anti-Microbial Resistant Global Threat. Int J Mol Sci 2021; 22:4042. [PMID: 33919847 PMCID: PMC8070759 DOI: 10.3390/ijms22084042] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 04/06/2021] [Accepted: 04/12/2021] [Indexed: 02/07/2023] Open
Abstract
Klebsiella pneumoniae (Kp) is an opportunistic pathogen and the leading cause of healthcare-associated infections, mostly affecting subjects with compromised immune systems or suffering from concurrent bacterial infections. However, the dramatic increase in hypervirulent strains and the emergence of new multidrug-resistant clones resulted in Kp occurrence among previously healthy people and in increased morbidity and mortality, including neonatal sepsis and death across low- and middle-income countries. As a consequence, carbapenem-resistant and extended spectrum β-lactamase-producing Kp have been prioritized as a critical anti-microbial resistance threat by the World Health Organization and this has renewed the interest of the scientific community in developing a vaccine as well as treatments alternative to the now ineffective antibiotics. Capsule polysaccharide is the most important virulence factor of Kp and plays major roles in the pathogenesis but its high variability (more than 100 different types have been reported) makes the identification of a universal treatment or prevention strategy very challenging. However, less variable virulence factors such as the O-Antigen, outer membrane proteins as fimbriae and siderophores might also be key players in the fight against Kp infections. Here, we review elements of the current status of the epidemiology and the molecular pathogenesis of Kp and explore specific bacterial antigens as potential targets for both prophylactic and therapeutic solutions.
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Affiliation(s)
| | | | | | | | - Francesca Micoli
- GSK Vaccines Institute for Global Health (GVGH) S.r.l., via Fiorentina 1, 53100 Siena, Italy; (V.A.); (M.M.R.); (G.G.); (F.B.S.)
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Abstract
The translocation of proteins across membranes is a fundamental cellular function. Bacteria have evolved a striking array of pathways for delivering proteins into or across cytoplasmic membranes and, when present, outer membranes. Translocated proteins can form part of the membrane landscape, reside in the periplasmic space situated between the inner and outer membranes of Gram-negative bacteria, deposit on the cell surface, or be released to the extracellular milieu or injected directly into target cells. One protein translocation system, the general secretory pathway, is conserved in all domains of life. A second, the twin-arginine translocation pathway, is also phylogenetically distributed among most bacteria and plant chloroplasts. While all cell types have evolved additional systems dedicated to the translocation of protein cargoes, the number of such systems in bacteria is now known to exceed nine. These dedicated protein translocation systems, which include the types 1 through 9 secretion systems (T1SSs-T9SSs), the chaperone-usher pathway, and type IV pilus system, are the subject of this review. Most of these systems were originally identified and have been extensively characterized in Gram-negative or diderm (two-membrane) species. It is now known that several of these systems also have been adapted to function in Gram-positive or monoderm (single-membrane) species, and at least one pathway is found only in monoderms. This review briefly summarizes the distinctive mechanistic and structural features of each dedicated pathway, as well as the shared properties, that together account for the broad biological diversity of protein translocation in bacteria.
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Affiliation(s)
- Peter J Christie
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St., Houston, TX, USA.
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Structural and Molecular Biology of a Protein-Polymerizing Nanomachine for Pilus Biogenesis. J Mol Biol 2017; 429:2654-2666. [PMID: 28551336 DOI: 10.1016/j.jmb.2017.05.016] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Revised: 05/16/2017] [Accepted: 05/17/2017] [Indexed: 01/23/2023]
Abstract
Bacteria produce protein polymers on their surface called pili or fimbriae that serve either as attachment devices or as conduits for secreted substrates. This review will focus on the chaperone-usher pathway of pilus biogenesis, a widespread assembly line for pilus production at the surface of Gram-negative bacteria and the archetypical protein-polymerizing nanomachine. Comparison with other nanomachines polymerizing other types of biological units, such as nucleotides during DNA replication, provides some unifying principles as to how multidomain proteins assemble biological polymers.
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Abstract
Strains of Klebsiella pneumoniae are frequently opportunistic pathogens implicated in urinary tract and catheter-associated urinary-tract infections of hospitalized patients and compromised individuals. Infections are particularly difficult to treat since most clinical isolates exhibit resistance to several antibiotics leading to treatment failure and the possibility of systemic dissemination. Infections of medical devices such as urinary catheters is a major site of K. pneumoniae infections and has been suggested to involve the formation of biofilms on these surfaces. Over the last decade there has been an increase in research activity designed to investigate the pathogenesis of K. pneumoniae in the urinary tract. These investigations have begun to define the bacterial factors that contribute to growth and biofilm formation. Several virulence factors have been demonstrated to mediate K. pneumoniae infectivity and include, but are most likely not limited to, adherence factors, capsule production, lipopolysaccharide presence, and siderophore activity. The development of both in vitro and in vivo models of infection will lead to further elucidation of the molecular pathogenesis of K. pneumoniae. As for most opportunistic infections, the role of host factors as well as bacterial traits are crucial in determining the outcome of infections. In addition, multidrug-resistant strains of these bacteria have become a serious problem in the treatment of Klebsiella infections and novel strategies to prevent and inhibit bacterial growth need to be developed. Overall, the frequency, significance, and morbidity associated with K. pneumoniae urinary tract infections have increased over many years. The emergence of these bacteria as sources of antibiotic resistance and pathogens of the urinary tract present a challenging problem for the clinician in terms of management and treatment of individuals.
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Dubreuil JD, Isaacson RE, Schifferli DM. Animal Enterotoxigenic Escherichia coli. EcoSal Plus 2016; 7:10.1128/ecosalplus.ESP-0006-2016. [PMID: 27735786 PMCID: PMC5123703 DOI: 10.1128/ecosalplus.esp-0006-2016] [Citation(s) in RCA: 165] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Indexed: 12/13/2022]
Abstract
Enterotoxigenic Escherichia coli (ETEC) is the most common cause of E. coli diarrhea in farm animals. ETEC are characterized by the ability to produce two types of virulence factors: adhesins that promote binding to specific enterocyte receptors for intestinal colonization and enterotoxins responsible for fluid secretion. The best-characterized adhesins are expressed in the context of fimbriae, such as the F4 (also designated K88), F5 (K99), F6 (987P), F17, and F18 fimbriae. Once established in the animal small intestine, ETEC produce enterotoxin(s) that lead to diarrhea. The enterotoxins belong to two major classes: heat-labile toxins that consist of one active and five binding subunits (LT), and heat-stable toxins that are small polypeptides (STa, STb, and EAST1). This review describes the disease and pathogenesis of animal ETEC, the corresponding virulence genes and protein products of these bacteria, their regulation and targets in animal hosts, as well as mechanisms of action. Furthermore, vaccines, inhibitors, probiotics, and the identification of potential new targets by genomics are presented in the context of animal ETEC.
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Affiliation(s)
- J Daniel Dubreuil
- Faculté de Médecine Vétérinaire, Université de Montréal, Québec J2S 7C6, Canada
| | - Richard E Isaacson
- Department of Veterinary and Biomedical Sciences, University of Minnesota, St. Paul, MN 55108
| | - Dieter M Schifferli
- School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104
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The pilus usher controls protein interactions via domain masking and is functional as an oligomer. Nat Struct Mol Biol 2015; 22:540-6. [PMID: 26052892 PMCID: PMC4496297 DOI: 10.1038/nsmb.3044] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Accepted: 05/12/2015] [Indexed: 12/21/2022]
Abstract
The chaperone-usher (CU) pathway assembles organelles termed pili or
fimbriae in Gram-negative bacteria. Type 1 pili expressed by uropathogenic
Escherichia coli are prototypical structures assembled by
the CU pathway. Biogenesis of pili by the CU pathway requires a periplasmic
chaperone and an outer membrane protein termed the usher (FimD). We show that
the FimD C-terminal domains provide the high-affinity substrate binding site,
but that these domains are masked in the resting usher. Domain masking requires
the FimD plug domain, which serves as a switch controlling usher activation. We
demonstrate that usher molecules can act in trans for pilus
biogenesis, providing conclusive evidence for a functional usher oligomer. These
results reveal mechanisms by which molecular machines such as the usher regulate
and harness protein-protein interactions, and suggest that ushers may interact
in a cooperative manner during pilus assembly in bacteria.
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Busch A, Phan G, Waksman G. Molecular mechanism of bacterial type 1 and P pili assembly. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2015; 373:rsta.2013.0153. [PMID: 25624519 DOI: 10.1098/rsta.2013.0153] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The formation of adhesive surface structures called pili or fimbriae ('bacterial hair') is an important contributor towards bacterial pathogenicity and persistence. To fight often chronic or recurrent bacterial infections such as urinary tract infections, it is necessary to understand the molecular mechanism of the nanomachines assembling such pili. Here, we focus on the so far best-known pilus assembly machinery: the chaperone-usher pathway producing the type 1 and P pili, and highlight the most recently acquired structural knowledge. First, we describe the subunits' structure and the molecular role of the periplasmic chaperone. Second, we focus on the outer-membrane usher structure and the catalytic mechanism of usher-mediated pilus biogenesis. Finally, we describe how the detailed understanding of the chaperone-usher pathway at a molecular level has paved the way for the design of a new generation of bacterial inhibitors called 'pilicides'.
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Affiliation(s)
- Andreas Busch
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK
| | - Gilles Phan
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK
| | - Gabriel Waksman
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK
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Geibel S, Waksman G. The molecular dissection of the chaperone–usher pathway. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1559-67. [DOI: 10.1016/j.bbamcr.2013.09.023] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Revised: 09/25/2013] [Accepted: 09/30/2013] [Indexed: 01/11/2023]
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Lillington J, Geibel S, Waksman G. Reprint of "Biogenesis and adhesion of type 1 and P pili". Biochim Biophys Acta Gen Subj 2014; 1850:554-64. [PMID: 25063559 DOI: 10.1016/j.bbagen.2014.07.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Revised: 04/22/2014] [Accepted: 04/24/2014] [Indexed: 12/20/2022]
Abstract
BACKGROUND Uropathogenic Escherichia coli (UPEC) cause urinary tract infections (UTIs) in approximately 50% of women. These bacteria use type 1 and P pili for host recognition and attachment. These pili are assembled by the chaperone-usher pathway of pilus biogenesis. SCOPE OF REVIEW The review examines the biogenesis and adhesion of the UPEC type 1 and P pili. Particular emphasis is drawn to the role of the outer membrane usher protein. The structural properties of the complete pilus are also examined to highlight the strength and functionality of the final assembly. MAJOR CONCLUSIONS The usher orchestrates the sequential addition of pilus subunits in a defined order. This process follows a subunit-incorporation cycle which consists of four steps: recruitment at the usher N-terminal domain, donor-strand exchange with the previously assembled subunit, transfer to the usher C-terminal domains and translocation of the nascent pilus. Adhesion by the type 1 and P pili is strengthened by the quaternary structure of their rod sections. The rod is endowed with spring-like properties which provide mechanical resistance against urine flow. The distal adhesins operate differently from one another, targeting receptors in a specific manner. The biogenesis and adhesion of type 1 and P pili are being therapeutically targeted, and efforts to prevent pilus growth or adherence are described. GENERAL SIGNIFICANCE The combination of structural and biochemical study has led to the detailed mechanistic understanding of this membrane spanning nano-machine. This can now be exploited to design novel drugs able to inhibit virulence. This is vital in the present era of resurgent antibiotic resistance. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.
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Affiliation(s)
- James Lillington
- Institute of Structural and Molecular Biology (ISMB), University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK
| | - Sebastian Geibel
- Institute of Structural and Molecular Biology (ISMB), University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK
| | - Gabriel Waksman
- Institute of Structural and Molecular Biology (ISMB), University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK.
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Lillington J, Geibel S, Waksman G. Biogenesis and adhesion of type 1 and P pili. Biochim Biophys Acta Gen Subj 2014; 1840:2783-93. [PMID: 24797039 DOI: 10.1016/j.bbagen.2014.04.021] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Revised: 04/22/2014] [Accepted: 04/24/2014] [Indexed: 01/22/2023]
Abstract
BACKGROUND Uropathogenic Escherichia coli (UPEC) cause urinary tract infections (UTIs) in approximately 50% of women. These bacteria use type 1 and P pili for host recognition and attachment. These pili are assembled by the chaperone-usher pathway of pilus biogenesis. SCOPE OF REVIEW The review examines the biogenesis and adhesion of the UPEC type 1 and P pili. Particular emphasis is drawn to the role of the outer membrane usher protein. The structural properties of the complete pilus are also examined to highlight the strength and functionality of the final assembly. MAJOR CONCLUSIONS The usher orchestrates the sequential addition of pilus subunits in a defined order. This process follows a subunit-incorporation cycle which consists of four steps: recruitment at the usher N-terminal domain, donor-strand exchange with the previously assembled subunit, transfer to the usher C-terminal domains and translocation of the nascent pilus. Adhesion by the type 1 and P pili is strengthened by the quaternary structure of their rod sections. The rod is endowed with spring-like properties which provide mechanical resistance against urine flow. The distal adhesins operate differently from one another, targeting receptors in a specific manner. The biogenesis and adhesion of type 1 and P pili are being therapeutically targeted, and efforts to prevent pilus growth or adherence are described. GENERAL SIGNIFICANCE The combination of structural and biochemical study has led to the detailed mechanistic understanding of this membrane spanning nano-machine. This can now be exploited to design novel drugs able to inhibit virulence. This is vital in the present era of resurgent antibiotic resistance. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.
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Affiliation(s)
- James Lillington
- Institute of Structural and Molecular Biology (ISMB), University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK
| | - Sebastian Geibel
- Institute of Structural and Molecular Biology (ISMB), University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK
| | - Gabriel Waksman
- Institute of Structural and Molecular Biology (ISMB), University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK.
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Ordered and ushered; the assembly and translocation of the adhesive type I and p pili. BIOLOGY 2013; 2:841-60. [PMID: 24833049 PMCID: PMC3960871 DOI: 10.3390/biology2030841] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Revised: 05/21/2013] [Accepted: 05/24/2013] [Indexed: 11/17/2022]
Abstract
Type I and P pili are chaperone-usher pili of uropathogenic Escherichia coli, which allow bacteria to adhere to host cell receptors. Pilus formation and secretion are orchestrated by two accessory proteins, a chaperone, which catalyses pilus subunit folding and maintains them in a polymerization-competent state, and an outer membrane-spanning nanomachine, the usher, which choreographs their assembly into a pilus and drives their secretion through the membrane. In this review, recent structures and kinetic studies are combined to examine the mechanism of type I and P pili assembly, as it is currently known. We also investigate how the knowledge of pilus biogenesis mechanisms has been exploited to design selective inhibitors of the process.
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Monteiro DCF, Kamdoum WVP, Paci E. Growth kinetics of bacterial pili from pairwise pilin association rates. PLoS One 2013; 8:e63065. [PMID: 23667575 PMCID: PMC3647068 DOI: 10.1371/journal.pone.0063065] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 03/27/2013] [Indexed: 11/18/2022] Open
Abstract
Bacterial pilogenesis is a remarkable example of biological non-templated self-assembly where a small number of different building blocks are arranged in a specific order resulting in a macroscopic hair-like fiber containing up to thousands copies of protein subunits. A number of advanced experimental techniques have been used to understand pilus growth. While details such as the conformation of the protein building blocks before and after the elementary polymerization step have enhanced our understanding of this mechanism, such information does not explain the high efficiency of this growth process. In this study, we focused on the growth of the Escherichia coli P-pilus, which is formed by the assembly of six subunits, structurally similar incomplete Ig-like domains. These subunits undergo polymerization through fold complementation by the donation of a β-sheet strand in a specific conserved order. All pairwise rates of association of the individual subunits with the corresponding β-sheet donor strand peptides have been previously determined through non-covalent mass-spectrometry. Here we use computational simulations to determine donor-strand exchange rates and subunit concentrations necessary to warrant the growth of pili showing similar lengths and subunit orders to those observed in vivo. Our findings confirm that additional factors must be involved in the modulation of the donor-strand exchange rate and/or pilin subunit concentration at the usher must be important for the precise ordering and rapid polymerization rates observed in vivo.
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Affiliation(s)
- Diana C. F. Monteiro
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | | | - Emanuele Paci
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
- * E-mail:
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FimA, FimF, and FimH are necessary for assembly of type 1 fimbriae on Salmonella enterica serovar Typhimurium. Infect Immun 2012; 80:3289-96. [PMID: 22778099 DOI: 10.1128/iai.00331-12] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Salmonella enterica serovar Typhimurium is a Gram-negative member of the family Enterobacteriaceae and is a common cause of bacterial food poisoning in humans. The fimbrial appendages are found on the surface of many enteric bacteria and enable the bacteria to bind to eukaryotic cells. S. Typhimurium type 1 fimbriae are characterized by mannose-sensitive hemagglutination and are assembled via the chaperone/usher pathway. S. Typhimurium type 1 fimbrial proteins are encoded by the fim gene cluster (fimAICDHFZYW), with fimAICDHF expressed as a single transcriptional unit. The structural components of the fimbriae are FimA (major subunit), FimI, FimH (adhesin), and FimF (adaptor). In order to determine which components are required for fimbrial formation in S. Typhimurium, mutations in fimA, fimI, fimH, and fimF were constructed and examined for their ability to produce surface-assembled fimbriae. S. Typhimurium SL1344ΔfimA, -ΔfimH, and -ΔfimF mutants were unable to assemble fimbriae, indicating that these genes are necessary for fimbrial production in S. Typhimurium. However, SL1344ΔfimI was able to assemble fimbriae. In Escherichia coli type 1 and Pap fimbriae, at least two adaptors are expressed in addition to the adhesins. However, E. coli type 1 and Pap fimbriae have been reported to be able to assemble fimbriae in the absence of these proteins. These results suggest differences between the S. Typhimurium type 1 fimbrial system and the E. coli type 1 and Pap fimbrial systems.
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