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Barringer R, Parnell AE, Lafita A, Monzon V, Back CR, Madej M, Potempa J, Nobbs AH, Burston SG, Bateman A, Race PR. Domain shuffling of a highly mutable ligand-binding fold drives adhesin generation across the bacterial kingdom. Proteins 2023; 91:1007-1020. [PMID: 36912614 PMCID: PMC10952558 DOI: 10.1002/prot.26487] [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: 11/11/2022] [Revised: 02/27/2023] [Accepted: 02/28/2023] [Indexed: 03/14/2023]
Abstract
Bacterial fibrillar adhesins are specialized extracellular polypeptides that promote the attachment of bacteria to the surfaces of other cells or materials. Adhesin-mediated interactions are critical for the establishment and persistence of stable bacterial populations within diverse environmental niches and are important determinants of virulence. The fibronectin (Fn)-binding fibrillar adhesin CshA, and its paralogue CshB, play important roles in host colonization by the oral commensal and opportunistic pathogen Streptococcus gordonii. As paralogues are often catalysts for functional diversification, we have probed the early stages of structural and functional divergence in Csh proteins by determining the X-ray crystal structure of the CshB adhesive domain NR2 and characterizing its Fn-binding properties in vitro. Despite sharing a common fold, CshB_NR2 displays an ~1.7-fold reduction in Fn-binding affinity relative to CshA_NR2. This correlates with reduced electrostatic charge in the Fn-binding cleft. Complementary bioinformatic studies reveal that homologues of CshA/B_NR2 domains are widely distributed in both Gram-positive and Gram-negative bacteria, where they are found housed within functionally cryptic multi-domain polypeptides. Our findings are consistent with the classification of Csh adhesins and their relatives as members of the recently defined polymer adhesin domain (PAD) family of bacterial proteins.
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Affiliation(s)
- Rob Barringer
- School of BiochemistryUniversity of Bristol, University WalkBristolBS8 1TDUK
| | - Alice E. Parnell
- School of BiochemistryUniversity of Bristol, University WalkBristolBS8 1TDUK
- BrisSynBio Synthetic Biology Research CentreUniversity of Bristol, Life Sciences BuildingTyndall AvenueBristolBS8 1TQUK
| | - Aleix Lafita
- European Molecular Biology LaboratoryEuropean Bioinformatics Institute (EMBL‐EBI)Wellcome Genome CampusHinxtonCB10 1SDUK
| | - Vivian Monzon
- European Molecular Biology LaboratoryEuropean Bioinformatics Institute (EMBL‐EBI)Wellcome Genome CampusHinxtonCB10 1SDUK
| | - Catherine R. Back
- School of BiochemistryUniversity of Bristol, University WalkBristolBS8 1TDUK
- BrisSynBio Synthetic Biology Research CentreUniversity of Bristol, Life Sciences BuildingTyndall AvenueBristolBS8 1TQUK
| | - Mariusz Madej
- Department of Microbiology, Faculty of Biochemistry, Biophysics, and BiotechnologyJagiellonian UniversityKrakowPoland
| | - Jan Potempa
- Department of Microbiology, Faculty of Biochemistry, Biophysics, and BiotechnologyJagiellonian UniversityKrakowPoland
- Department of Oral Immunology and Infectious DiseasesUniversity of Louisville School of DentistryLouisvilleKentuckyUSA
| | - Angela H. Nobbs
- Bristol Dental School, University of BristolLower Maudlin StreetBristolBS1 2LYUK
| | - Steven G. Burston
- School of BiochemistryUniversity of Bristol, University WalkBristolBS8 1TDUK
| | - Alex Bateman
- European Molecular Biology LaboratoryEuropean Bioinformatics Institute (EMBL‐EBI)Wellcome Genome CampusHinxtonCB10 1SDUK
| | - Paul R. Race
- School of BiochemistryUniversity of Bristol, University WalkBristolBS8 1TDUK
- BrisSynBio Synthetic Biology Research CentreUniversity of Bristol, Life Sciences BuildingTyndall AvenueBristolBS8 1TQUK
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The long and the short of Periscope Proteins. Biochem Soc Trans 2022; 50:1293-1302. [PMID: 36196877 DOI: 10.1042/bst20220194] [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: 07/26/2022] [Revised: 09/10/2022] [Accepted: 09/13/2022] [Indexed: 11/17/2022]
Abstract
Bacteria sense, interact with, and modify their environmental niche by deploying a molecular ensemble at the cell surface. The changeability of this exposed interface, combined with extreme changes in the functional repertoire associated with lifestyle switches from planktonic to adherent and biofilm states necessitate dynamic variability. Dynamic surface changes include chemical modifications to the cell wall; export of diverse extracellular biofilm components; and modulation of expression of cell surface proteins for adhesion, co-aggregation and virulence. Local enrichment for highly repetitive proteins with high tandem repeat identity has been an enigmatic phenomenon observed in diverse bacterial species. Preliminary observations over decades of research suggested these repeat regions were hypervariable, as highly related strains appeared to express homologues with diverse molecular mass. Long-read sequencing data have been interrogated to reveal variation in repeat number; in combination with structural, biophysical and molecular dynamics approaches, the Periscope Protein class has been defined for cell surface attached proteins that dynamically expand and contract tandem repeat tracts at the population level. Here, I review the diverse high-stability protein folds and coherent interdomain linkages culminating in the formation of highly anisotropic linear repeat arrays, so-called rod-like protein 'stalks', supporting roles in bacterial adhesion, biofilm formation, cell surface spatial competition, and immune system modulation. An understanding of the functional impacts of dynamic changes in repeat arrays and broader characterisation of the unusual protein folds underpinning this variability will help with the design of immunisation strategies, and contribute to synthetic biology approaches including protein engineering and microbial consortia construction.
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Lima BP, Davies JR, Wickström C, Johnstone KF, Hall JW, Svensater G, Herzberg MC. Streptococcus gordonii Poised for Glycan Feeding through a MUC5B-Discriminating, Lipoteichoic Acid-Mediated Outside-In Signaling Circuit. J Bacteriol 2022; 204:e0011822. [PMID: 35652671 PMCID: PMC9210975 DOI: 10.1128/jb.00118-22] [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: 03/30/2022] [Accepted: 05/09/2022] [Indexed: 11/20/2022] Open
Abstract
Many oral bacteria employ cell wall-anchored adhesins to bind to the salivary films coating the teeth and mucosal surfaces. Surface binding prevents clearance and facilitates catabolism of salivary film glycoproteins. We asked whether Streptococcus gordonii adhesin expression changes in response to surface salivary cues using a eukaryote-like, outside-in recognition and signaling circuit. To determine whether the cues were discriminated, S. gordonii was tested during cell adhesion and biofilm formation on a MUC5B-rich or lower-molecular-mass salivary fraction or an uncoated abiotic surface. Cells were recovered and analyzed for differences in gene expression and proteins in cell wall fractions. In salivary-free conditions, planktonic S. gordonii presented three prominent cell wall LPXTG-motif proteins, SGO_1487, SGO_0890, and MbpA (mucin-binding protein A; SGO_0707). During biofilm formation on MUC5B-coated surfaces, MbpA, a MUC5B-binding protein, and key genes in the tagatose and quorum-sensing pathways were strongly promoted. The response to MUC5B required the two-component system (TCS), streptococcal regulator of adhesins sensor and regulator (SraSR, SGO_1180/81), lipoteichoic acid (LTA), and the homologous paired adhesins, SspA and SspB (SspAB). LTA appears to link the outside signal (MUC5B) to intramembrane SraSR. Tagatose pathway gene expression may poise cells to metabolize MUC5B glycans and, with a quorum-sensing gene (luxS), may direct formation of a consortium to facilitate glycan cross-feeding by S. gordonii. We now show that a Gram-positive bacterium discriminates specific surface environmental cues using an outside-in signaling mechanism to apparently optimize colonization of saliva-coated surfaces. IMPORTANCE All organisms throughout the tree of life sense and respond to their surface environments. To discriminate among mucosal surface environmental cues, we report that Streptococcus gordonii recognizes a high-molecular-weight mucin glycoprotein, MUC5B, using the paired adhesins SspAB and lipoteichoic acid; the latter bridges the outside signal to an intramembrane two-component system to transcriptionally regulate a MUC5B-specific adhesin and genes that may facilitate glycan catabolism.
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Affiliation(s)
- Bruno P. Lima
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA
| | - Julia R. Davies
- Section for Oral Biology and Pathology, Faculty of Odontology, Malmö University, Malmö, Sweden
| | - Claes Wickström
- Section for Oral Biology and Pathology, Faculty of Odontology, Malmö University, Malmö, Sweden
| | - Karen F. Johnstone
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA
| | - Jeffrey W. Hall
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA
| | - Gunnel Svensater
- Section for Oral Biology and Pathology, Faculty of Odontology, Malmö University, Malmö, Sweden
| | - Mark C. Herzberg
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA
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Periscope Proteins are variable-length regulators of bacterial cell surface interactions. Proc Natl Acad Sci U S A 2021; 118:2101349118. [PMID: 34074781 PMCID: PMC8201768 DOI: 10.1073/pnas.2101349118] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The structure of single and tandem SHIRT domains from the streptococcal surface protein Sgo_0707 were determined. In conjunction with biophysics and molecular dynamics simulations, the results show that the observed gene length variation would result in differential projection of the host ligand binding domain on the bacterial cell surface. An analysis of long-read DNA sequence data reveals many other repetitive bacterial surface proteins that appear to undergo gene length variation. We propose that these variable-length “Periscope Proteins” represent an important mechanism of bacterial cell surface modification with potential roles in infection and immune evasion. Changes at the cell surface enable bacteria to survive in dynamic environments, such as diverse niches of the human host. Here, we reveal “Periscope Proteins” as a widespread mechanism of bacterial surface alteration mediated through protein length variation. Tandem arrays of highly similar folded domains can form an elongated rod-like structure; thus, variation in the number of domains determines how far an N-terminal host ligand binding domain projects from the cell surface. Supported by newly available long-read genome sequencing data, we propose that this class could contain over 50 distinct proteins, including those implicated in host colonization and biofilm formation by human pathogens. In large multidomain proteins, sequence divergence between adjacent domains appears to reduce interdomain misfolding. Periscope Proteins break this “rule,” suggesting that their length variability plays an important role in regulating bacterial interactions with host surfaces, other bacteria, and the immune system.
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Arora S, Gordon J, Hook M. Collagen Binding Proteins of Gram-Positive Pathogens. Front Microbiol 2021; 12:628798. [PMID: 33613497 PMCID: PMC7893114 DOI: 10.3389/fmicb.2021.628798] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Accepted: 01/11/2021] [Indexed: 12/12/2022] Open
Abstract
Collagens are the primary structural components of mammalian extracellular matrices. In addition, collagens regulate tissue development, regeneration and host defense through interaction with specific cellular receptors. Their unique triple helix structure, which requires a glycine residue every third amino acid, is the defining structural feature of collagens. There are 28 genetically distinct collagens in humans. In addition, several other unrelated human proteins contain a collagen domain. Gram-positive bacteria of the genera Staphylococcus, Streptococcus, Enterococcus, and Bacillus express cell surface proteins that bind to collagen. These proteins of Gram-positive pathogens are modular proteins that can be classified into different structural families. This review will focus on the different structural families of collagen binding proteins of Gram-positive pathogen. We will describe how these proteins interact with the triple helix in collagens and other host proteins containing a collagenous domain and discuss how these interactions can contribute to the pathogenic processes.
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Affiliation(s)
- Srishtee Arora
- Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M Health Science Center, Houston, TX, United States
| | - Jay Gordon
- Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M Health Science Center, Houston, TX, United States
| | - Magnus Hook
- Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M Health Science Center, Houston, TX, United States
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Uncovering Roles of Streptococcus gordonii SrtA-Processed Proteins in the Biofilm Lifestyle. J Bacteriol 2020; 203:JB.00544-20. [PMID: 33106345 DOI: 10.1128/jb.00544-20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 10/20/2020] [Indexed: 12/12/2022] Open
Abstract
Streptococcus gordonii is a commensal oral organism. Harmless in the oral cavity, S. gordonii is an opportunistic pathogen. S. gordonii adheres to body surfaces using surface adhesive proteins (adhesins), which are critical to subsequent formation of biofilm communities. As in most Gram-positive bacteria, S. gordonii surface proteins containing the C-terminal LPXTG motif cleavage sequence are processed by sortase A (SrtA) to become covalently attached to the cell wall. To characterize the functional diversity and redundancy in the family of SrtA-processed proteins, an S. gordonii DL1 markerless deletion mutant library was constructed of each of the 26 putative SrtA-processed proteins. Each library member was evaluated for growth in rich medium, biofilm formation on plastic, saliva and salivary fractions, cell surface hydrophobicity (CSH), hemagglutination, and integration into an ex vivo plaque biofilm community. Library members were compared to the non-SrtA-processed adhesins AbpA and AbpB. While no major growth differences in rich medium were observed, many S. gordonii LPXTG/A proteins impacted biofilm formation on one or more of the substrates. Several mutants showed significant differences in hemagglutination, hydrophobicity, or fitness in the ex vivo plaque model. From the identification of redundant and unique functions in these in vitro and ex vivo systems, functional stratification among the LPXTG/A proteins is apparent.IMPORTANCE S. gordonii interactions with its environment depend on the complement of cell wall proteins. A subset of these cell wall proteins requires processing by the enzyme sortase A (SrtA). The identification of SrtA-processed proteins and their functional characterization will help the community to better understand how S. gordonii engages with its surroundings, including other microbes, integrates into the plaque community, adheres to the tooth surface, and hematogenously disseminates to cause blood-borne infections. This study identified 26 putative SrtA-processed proteins through creation of a markerless deletion mutant library. The library was subject to functional screens that were chosen to better understand key aspects of S. gordonii physiology and pathogenesis.
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Hoffmann L, Anders K, Bischof LF, Ye X, Reimann J, Khadouma S, Pham TK, van der Does C, Wright PC, Essen LO, Albers SV. Structure and interactions of the archaeal motility repression module ArnA–ArnB that modulates archaellum gene expression in Sulfolobus acidocaldarius. J Biol Chem 2019; 294:7460-7471. [PMID: 30902813 PMCID: PMC6509490 DOI: 10.1074/jbc.ra119.007709] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2019] [Revised: 03/20/2019] [Indexed: 11/06/2022] Open
Abstract
Phosphorylation-dependent interactions play crucial regulatory roles in all domains of life. Forkhead-associated (FHA) and von Willebrand type A (vWA) domains are involved in several phosphorylation-dependent processes of multiprotein complex assemblies. Although well-studied in eukaryotes and bacteria, the structural and functional contexts of these domains are not yet understood in Archaea. Here, we report the structural base for such an interacting pair of FHA and vWA domain-containing proteins, ArnA and ArnB, in the thermoacidophilic archaeon Sulfolobus acidocaldarius, where they act synergistically and negatively modulate motility. The structure of the FHA domain of ArnA at 1.75 Å resolution revealed that it belongs to the subclass of FHA domains, which recognizes double-pSer/pThr motifs. We also solved the 1.5 Å resolution crystal structure of the ArnB paralog vWA2, disclosing a complex topology comprising the vWA domain, a β-sandwich fold, and a C-terminal helix bundle. We further show that ArnA binds to the C terminus of ArnB, which harbors all the phosphorylation sites identified to date and is important for the function of ArnB in archaellum regulation. We also observed that expression levels of the archaellum components in response to changes in nutrient conditions are independent of changes in ArnA and ArnB levels and that a strong interaction between ArnA and ArnB observed during growth on rich medium sequentially diminishes after nutrient limitation. In summary, our findings unravel the structural features in ArnA and ArnB important for their interaction and functional archaellum expression and reveal how nutrient conditions affect this interaction.
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Affiliation(s)
- Lena Hoffmann
- From the Institute for Biology II, Molecular Biology of Archaea and
| | - Katrin Anders
- the Philipps University, Department of Chemistry, 35032 Marburg, Germany
| | - Lisa F Bischof
- From the Institute for Biology II, Molecular Biology of Archaea and
- the Spemann Graduate School of Biology and Medicine, University of Freiburg, 79104 Freiburg, Germany
| | - Xing Ye
- From the Institute for Biology II, Molecular Biology of Archaea and
| | - Julia Reimann
- From the Institute for Biology II, Molecular Biology of Archaea and
| | - Sunia Khadouma
- From the Institute for Biology II, Molecular Biology of Archaea and
| | - Trong K Pham
- the ChELSI Institute, Department of Chemical and Biological Engineering, University of Sheffield, Sheffield S1 3JD, United Kingdom, and
| | | | - Phillip C Wright
- the Faculty of Science, Agriculture and Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
| | - Lars-Oliver Essen
- the Philipps University, Department of Chemistry, 35032 Marburg, Germany,
- the LOEWE Center for Synthetic Microbiology, 35043 Marburg, Germany
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Patel S, Mathivanan N, Goyal A. Bacterial adhesins, the pathogenic weapons to trick host defense arsenal. Biomed Pharmacother 2017; 93:763-771. [DOI: 10.1016/j.biopha.2017.06.102] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Revised: 06/23/2017] [Accepted: 06/29/2017] [Indexed: 12/18/2022] Open
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Back CR, Sztukowska MN, Till M, Lamont RJ, Jenkinson HF, Nobbs AH, Race PR. The Streptococcus gordonii Adhesin CshA Protein Binds Host Fibronectin via a Catch-Clamp Mechanism. J Biol Chem 2017; 292:1538-1549. [PMID: 27920201 PMCID: PMC5290933 DOI: 10.1074/jbc.m116.760975] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 12/01/2016] [Indexed: 11/06/2022] Open
Abstract
Adherence of bacteria to biotic or abiotic surfaces is a prerequisite for host colonization and represents an important step in microbial pathogenicity. This attachment is facilitated by bacterial adhesins at the cell surface. Because of their size and often elaborate multidomain architectures, these polypeptides represent challenging targets for detailed structural and functional characterization. The multifunctional fibrillar adhesin CshA, which mediates binding to both host molecules and other microorganisms, is an important determinant of colonization by Streptococcus gordonii, an oral commensal and opportunistic pathogen of animals and humans. CshA binds the high-molecular-weight glycoprotein fibronectin (Fn) via an N-terminal non-repetitive region, and this protein-protein interaction has been proposed to promote S. gordonii colonization at multiple sites within the host. However, the molecular details of how these two proteins interact have yet to be established. Here we present a structural description of the Fn binding N-terminal region of CshA, derived from a combination of X-ray crystallography, small angle X-ray scattering, and complementary biophysical methods. In vitro binding studies support a previously unreported two-state "catch-clamp" mechanism of Fn binding by CshA, in which the disordered N-terminal domain of CshA acts to "catch" Fn, via formation of a rapidly assembled but also readily dissociable pre-complex, enabling its neighboring ligand binding domain to tightly clamp the two polypeptides together. This study presents a new paradigm for target binding by a bacterial adhesin, the identification of which will inform future efforts toward the development of anti-adhesive agents that target S. gordonii and related streptococci.
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Affiliation(s)
- Catherine R Back
- From the School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, United Kingdom
| | - Maryta N Sztukowska
- the Department of Oral Immunology and Infectious Diseases, University of Louisville, Louisville, Kentucky 40202; the Department of Dentistry, University of Information Technology and Management, 35-225 Rzeszow, Poland
| | - Marisa Till
- the School of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom; the BrisSynBio Synthetic Biology Research Centre, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol, BS8 1TQ, United Kingdom
| | - Richard J Lamont
- the Department of Oral Immunology and Infectious Diseases, University of Louisville, Louisville, Kentucky 40202
| | - Howard F Jenkinson
- From the School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, United Kingdom
| | - Angela H Nobbs
- From the School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, United Kingdom.
| | - Paul R Race
- the School of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom; the BrisSynBio Synthetic Biology Research Centre, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol, BS8 1TQ, United Kingdom.
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Kang HJ, Paterson NG, Kim CU, Middleditch M, Chang C, Ton-That H, Baker EN. A slow-forming isopeptide bond in the structure of the major pilin SpaD from Corynebacterium diphtheriae has implications for pilus assembly. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2014; 70:1190-201. [PMID: 24816089 PMCID: PMC4014117 DOI: 10.1107/s1399004714001400] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Accepted: 01/20/2014] [Indexed: 12/04/2022]
Abstract
The Gram-positive organism Corynebacterium diphtheriae, the cause of diphtheria in humans, expresses pili on its surface which it uses for adhesion and colonization of its host. These pili are covalent protein polymers composed of three types of pilin subunit that are assembled by specific sortase enzymes. A structural analysis of the major pilin SpaD, which forms the polymeric backbone of one of the three types of pilus expressed by C. diphtheriae, is reported. Mass-spectral and crystallographic analysis shows that SpaD contains three internal Lys-Asn isopeptide bonds. One of these, shown by mass spectrometry to be located in the N-terminal D1 domain of the protein, only forms slowly, implying an energy barrier to bond formation. Two crystal structures, of the full-length three-domain protein at 2.5 Å resolution and of a two-domain (D2-D3) construct at 1.87 Å resolution, show that each of the three Ig-like domains contains a single Lys-Asn isopeptide-bond cross-link, assumed to give mechanical stability as in other such pili. Additional stabilizing features include a disulfide bond in the D3 domain and a calcium-binding loop in D2. The N-terminal D1 domain is more flexible than the others and, by analogy with other major pilins of this type, the slow formation of its isopeptide bond can be attributed to its location adjacent to the lysine used in sortase-mediated polymerization during pilus assembly.
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Affiliation(s)
- Hae Joo Kang
- Maurice Wilkins Centre for Molecular Biodiscovery and School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
| | - Neil G. Paterson
- Maurice Wilkins Centre for Molecular Biodiscovery and School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
| | - Chae Un Kim
- Cornell High Energy Synchrotron Source and Macromolecular Diffraction Facility at CHESS (MacCHESS), Cornell University, Ithaca, NY 14853, USA
| | - Martin Middleditch
- Maurice Wilkins Centre for Molecular Biodiscovery and School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
| | - Chungyu Chang
- Department of Microbiology and Molecular Genetics, University of Texas–Houston Medical School, Houston, TX 77030, USA
| | - Hung Ton-That
- Department of Microbiology and Molecular Genetics, University of Texas–Houston Medical School, Houston, TX 77030, USA
| | - Edward N. Baker
- Maurice Wilkins Centre for Molecular Biodiscovery and School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
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