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Singh AK, Murmu S, Krężel A. One-Step Sortase-Mediated Chemoenzymatic Semisynthesis of Deubiquitinase-Resistant Ub-Peptide Conjugates. ACS OMEGA 2022; 7:46693-46701. [PMID: 36570257 PMCID: PMC9773336 DOI: 10.1021/acsomega.2c05652] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 11/23/2022] [Indexed: 06/17/2023]
Abstract
Post-translational modifications (PTMs) of proteins increase the functional diversity of the proteome and play crucial regulatory roles in cellular processes. Ubiquitination is a highly regulated and reversible PTM accomplished by a complex multistep process with the sequential action of several specific ubiquitinating (E1-E3) and deubiquitinating enzymes. The different types of ubiquitination (mono-, poly-mono-, and poly-) and the presence of several target sites in a single substrate add to its complexity, which makes the in vitro reconstitution of this ubiquitin (Ub) machinery a quite cumbersome process. Defects in components of the ubiquitination process also contribute to disease pathogenesis, especially cancer and neurodegeneration. This makes them of interest as potential therapeutic targets. Therefore, the development of efficient and reliable methods that will generate a highly homogeneous ubiquitinated peptide and protein conjugate is a topical subject area of research. In this report, we describe the development of a simple and efficient in vitro sortase-mediated chemoenzymatic strategy for semisynthesis of defined and homogeneous ubiquitin conjugates with more than 90% yield. This was achieved by engineering a sortase recognition motif in the dynamic C-terminus of ubiquitin and its conjugation to an isopeptide-linked di-Gly appended peptide LMFK(ε-GG)TEG corresponding to the ubiquitination site residues 383LMFKTEG389 of p53. The defined and homogeneous ubiquitin conjugates were also weighed for their recognition propensity by deubiquitinating enzymes. This facile semisynthesis of ubiquitin conjugates establishes a simple one-step sortase-mediated chemoenzymatic route for the synthesis of homogeneous and defined isopeptide-linked polypeptides and will help in understanding the complexity of the ubiquitination machinery as well as designing isopeptide drugs and therapeutics.
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Affiliation(s)
- Avinash K. Singh
- Department
of Chemical Biology, Faculty of Biotechnology, University of Wrocław, F. Joliot-Curie 14a, 50-383 Wrocław, Poland
- National
Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110067, India
| | - Sumit Murmu
- National
Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110067, India
| | - Artur Krężel
- Department
of Chemical Biology, Faculty of Biotechnology, University of Wrocław, F. Joliot-Curie 14a, 50-383 Wrocław, Poland
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2
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A conserved signal-peptidase antagonist modulates membrane homeostasis of actinobacterial sortase critical for surface morphogenesis. Proc Natl Acad Sci U S A 2022; 119:e2203114119. [PMID: 35787040 PMCID: PMC9282373 DOI: 10.1073/pnas.2203114119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cell wall anchoring of surface proteins in Gram-positive bacteria requires a sortase enzyme. Here, we unveiled the hitherto unknown function of an evolutionarily conserved small transmembrane protein, named SafA, genetically linked to the housekeeping sortase in Actinobacteria. We show that Actinomyces oris SafA interacts with the housekeeping sortase SrtA via the conserved FPW motif and prevents SrtA cleavage by the signal peptidase LepB2, hence maintaining membrane homeostasis of SrtA. This function is conserved as ectopic expression of SafA from Corynebacterium diphtheriae and Corynebacterium matruchotii in the A. oris safA mutant rescues its defects in cell morphology, pilus assembly, surface protein localization, and polymicrobial interactions. Thus, SafA represents an archetypal antagonist of signal peptidase that modulates surface assembly in Actinobacteria. Most Actinobacteria encode a small transmembrane protein, whose gene lies immediately downstream of the housekeeping sortase coding for a transpeptidase that anchors many extracellular proteins to the Gram-positive bacterial cell wall. Here, we uncover the hitherto unknown function of this class of conserved proteins, which we name SafA, as a topological modulator of sortase in the oral Actinobacterium Actinomyces oris. Genetic deletion of safA induces cleavage and excretion of the otherwise predominantly membrane-bound SrtA in wild-type cells. Strikingly, the safA mutant, although viable, exhibits severe abnormalities in cell morphology, pilus assembly, surface protein localization, and polymicrobial interactions—the phenotypes that are mirrored by srtA depletion. The pleiotropic defect of the safA mutant is rescued by ectopic expression of safA from not only A. oris, but also Corynebacterium diphtheriae or Corynebacterium matruchotii. Importantly, the SrtA N terminus harbors a tripartite-domain feature typical of a bacterial signal peptide, including a cleavage motif AXA, mutations in which prevent SrtA cleavage mediated by the signal peptidase LepB2. Bacterial two-hybrid analysis demonstrates that SafA and SrtA directly interact. This interaction involves a conserved motif FPW within the exoplasmic face of SafA, since mutations of this motif abrogate SafA-SrtA interaction and induce SrtA cleavage and excretion as observed in the safA mutant. Evidently, SafA is a membrane-imbedded antagonist of signal peptidase that safeguards and maintains membrane homeostasis of the housekeeping sortase SrtA, a central player of cell surface assembly.
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3
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Chang C, Wu C, Osipiuk J, Siegel SD, Zhu S, Liu X, Joachimiak A, Clubb RT, Das A, Ton-That H. Cell-to-cell interaction requires optimal positioning of a pilus tip adhesin modulated by gram-positive transpeptidase enzymes. Proc Natl Acad Sci U S A 2019; 116:18041-18049. [PMID: 31427528 PMCID: PMC6731673 DOI: 10.1073/pnas.1907733116] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Assembly of pili on the gram-positive bacterial cell wall involves 2 conserved transpeptidase enzymes named sortases: One for polymerization of pilin subunits and another for anchoring pili to peptidoglycan. How this machine controls pilus length and whether pilus length is critical for cell-to-cell interactions remain unknown. We report here in Actinomyces oris, a key colonizer in the development of oral biofilms, that genetic disruption of its housekeeping sortase SrtA generates exceedingly long pili, catalyzed by its pilus-specific sortase SrtC2 that possesses both pilus polymerization and cell wall anchoring functions. Remarkably, the srtA-deficient mutant fails to mediate interspecies interactions, or coaggregation, even though the coaggregation factor CafA is present at the pilus tip. Increasing ectopic expression of srtA in the mutant progressively shortens pilus length and restores coaggregation accordingly, while elevated levels of shaft pilins and SrtC2 produce long pili and block coaggregation by SrtA+ bacteria. With structural studies, we uncovered 2 key structural elements in SrtA that partake in recognition of pilin substrates and regulate pilus length by inducing the capture and transfer of pilus polymers to the cell wall. Evidently, coaggregation requires proper positioning of the tip adhesin CafA via modulation of pilus length by the housekeeping sortase SrtA.
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Affiliation(s)
- Chungyu Chang
- Division of Oral Biology and Medicine, School of Dentistry, University of California, Los Angeles, CA 90095;
| | - Chenggang Wu
- Department of Microbiology & Molecular Genetics, University of Texas Health Science Center, Houston, TX 77030
| | - Jerzy Osipiuk
- Center for Structural Genomics of Infectious Diseases, Consortium for Advanced Science and Engineering, University of Chicago, Chicago, IL 60637
- Structural Biology Center, Argonne National Laboratory, Lemont, IL 60439
| | - Sara D Siegel
- Department of Microbiology & Molecular Genetics, University of Texas Health Science Center, Houston, TX 77030
| | - Shiwei Zhu
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06510
| | - Xiangan Liu
- Department of Microbiology & Molecular Genetics, University of Texas Health Science Center, Houston, TX 77030
| | - Andrzej Joachimiak
- Center for Structural Genomics of Infectious Diseases, Consortium for Advanced Science and Engineering, University of Chicago, Chicago, IL 60637
- Structural Biology Center, Argonne National Laboratory, Lemont, IL 60439
| | - Robert T Clubb
- Department of Chemistry and Biochemistry, University of California, Los Angeles-Department of Energy Institute of Genomics and Proteomics, University of California, Los Angeles, CA 90095
| | - Asis Das
- Department of Medicine, Neag Comprehensive Cancer Center, University of Connecticut Health Center, Farmington, CT 06030
| | - Hung Ton-That
- Division of Oral Biology and Medicine, School of Dentistry, University of California, Los Angeles, CA 90095;
- Molecular Biology Institute, University of California, Los Angeles, CA 90095
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4
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Megta AK, Mishra AK, Palva A, von Ossowski I, Krishnan V. Crystal structure of basal pilin SpaE reveals the molecular basis of its incorporation in the lactobacillar SpaFED pilus. J Struct Biol 2019; 207:74-84. [PMID: 31026587 DOI: 10.1016/j.jsb.2019.04.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2019] [Revised: 04/15/2019] [Accepted: 04/23/2019] [Indexed: 11/16/2022]
Abstract
For some Gram-positive genera and species, the long-extended and adhesive sortase-dependent pilus plays an essential role during host colonization, biofilm formation, and immune modulation. Lactobacillus rhamnosus GG is a gut-adapted commensal strain that harbors the operonic genes for the SpaCBA and SpaFED pili, both being comprised of three different protein subunits termed the backbone, tip, and basal pilins. Crystal structures of the backbone pilins (SpaA and SpaD) have recently been solved, and here we describe the high-resolution (1.5 Å) structural determination of the SpaE basal pilin. SpaE consists of two immunoglobulin-like CnaB domains, with each displaying a spontaneously formed internal isopeptide bond, though apparently slow forming in the N-terminal domain. Remarkably, SpaE contains an atypically lengthy unstructured C-terminal tail, along with an YPKN pilin motif peptide, which is normally reserved for backbone subunits. Based on our analysis of the crystal structure data, we provide a molecular model for the basal positioning of the SpaE pilin within the SpaFED pilus.
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Affiliation(s)
- Abhin Kumar Megta
- Laboratory of Structural Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Faridabad, Haryana 121 001, India; School of Biotechnology, KIIT University, Odisha 751024, India
| | - Arjun K Mishra
- Laboratory of Structural Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Faridabad, Haryana 121 001, India
| | - Airi Palva
- Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland
| | | | - Vengadesan Krishnan
- Laboratory of Structural Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Faridabad, Haryana 121 001, India.
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5
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Sortases, Surface Proteins, and Their Roles in Staphylococcus aureus Disease and Vaccine Development. Microbiol Spectr 2019; 7. [PMID: 30737913 DOI: 10.1128/microbiolspec.psib-0004-2018] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Sortases cleave short peptide motif sequences at the C-terminal end of secreted surface protein precursors and either attach these polypeptides to the peptidoglycan of Gram-positive bacteria or promote their assembly into pilus structures that are also attached to peptidoglycan. Sortase A, the enzyme first identified in the human pathogen Staphylococcus aureus, binds LPXTG motif sorting signals, cleaves between threonine (T) and glycine (G) residues, and forms an acyl enzyme between its active-site cysteine thiol and the carboxyl group of threonine (T). Sortase A acyl enzyme is relieved by the nucleophilic attack of the cross bridge amino group within lipid II, thereby generating surface protein linked to peptidoglycan precursor. Such products are subsequently incorporated into the cell wall envelope by enzymes of the peptidoglycan synthesis pathway. Surface proteins linked to peptidoglycan may be released from the bacterial envelope to diffuse into host tissues and fulfill specific biological functions. S. aureus sortase A is essential for host colonization and for the pathogenesis of invasive diseases. Staphylococcal sortase-anchored surface proteins fulfill key functions during the infectious process, and vaccine-induced antibodies targeting surface proteins may provide protection against S. aureus. Alternatively, small-molecule inhibitors of sortase may be useful agents for the prevention of S. aureus colonization and invasive disease.
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6
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Anchoring of LPXTG-Like Proteins to the Gram-Positive Cell Wall Envelope. Curr Top Microbiol Immunol 2017; 404:159-175. [PMID: 27097813 DOI: 10.1007/82_2016_8] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In Gram-positive bacteria, protein precursors with a signal peptide and a cell wall sorting signal (CWSS)-which begins with an LPXTG motif, followed by a hydrophobic domain and a tail of positively charged residues-are targeted to the cell envelope by a transpeptidase enzyme call sortase. Evolution and selective pressure gave rise to six classes of sortase, i.e., SrtA-F. Only class C sortases are capable of polymerizing substrates harboring the pilin motif and CWSS into protein polymers known as pili or fimbriae, whereas the others perform cell wall anchoring functions. Regardless of the products generated from these sortases, the basic principle of sortase-catalyzed transpeptidation is the same. It begins with the cleavage of the LPXTG motif, followed by the cross-linking of this cleaved product at the threonine residue to a nucleophile, i.e., an active amino group of the peptidoglycan stem peptide or the lysine residue of the pilin motif. This chapter will summarize the efforts to identify and characterize sortases and their associated pathways with emphasis on the cell wall anchoring function.
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7
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von Ossowski I. Novel Molecular Insights about Lactobacillar Sortase-Dependent Piliation. Int J Mol Sci 2017; 18:ijms18071551. [PMID: 28718795 PMCID: PMC5536039 DOI: 10.3390/ijms18071551] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Revised: 07/11/2017] [Accepted: 07/14/2017] [Indexed: 01/09/2023] Open
Abstract
One of the more conspicuous structural features that punctuate the outer cell surface of certain bacterial Gram-positive genera and species is the sortase-dependent pilus. As these adhesive and variable-length protrusions jut outward from the cell, they provide a physically expedient and useful means for the initial contact between a bacterium and its ecological milieu. The sortase-dependent pilus displays an elongated macromolecular architecture consisting of two to three types of monomeric protein subunits (pilins), each with their own specific function and location, and that are joined together covalently by the transpeptidyl activity of a pilus-specific C-type sortase enzyme. Sortase-dependent pili were first detected among the Gram-positive pathogens and subsequently categorized as an essential virulence factor for host colonization and tissue invasion by these harmful bacteria. However, the sortase-dependent pilus was rebranded as also a niche-adaptation factor after it was revealed that “friendly” Gram-positive commensals exhibit the same kind of pilus structures, which includes two contrasting gut-adapted species from the Lactobacillus genus, allochthonous Lactobacillus rhamnosus and autochthonous Lactobacillus ruminis. This review will highlight and discuss what has been learned from the latest research carried out and published on these lactobacillar pilus types.
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Affiliation(s)
- Ingemar von Ossowski
- Department of Veterinary Biosciences, Faculty of Veterinary Medicine, University of Helsinki, Helsinki FIN-00014, Finland.
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8
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Electron Transport Chain Is Biochemically Linked to Pilus Assembly Required for Polymicrobial Interactions and Biofilm Formation in the Gram-Positive Actinobacterium Actinomyces oris. mBio 2017. [PMID: 28634238 PMCID: PMC5478893 DOI: 10.1128/mbio.00399-17] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The Gram-positive actinobacteria Actinomyces spp. are key colonizers in the development of oral biofilms due to the inherent ability of Actinomyces to adhere to receptor polysaccharides on the surface of oral streptococci and host cells. This receptor-dependent bacterial interaction, or coaggregation, requires a unique sortase-catalyzed pilus consisting of the pilus shaft FimA and the coaggregation factor CafA forming the pilus tip. While the essential role of the sortase machine SrtC2 in pilus assembly, biofilm formation, and coaggregation has been established, little is known about trans-acting factors contributing to these processes. We report here a large-scale Tn5 transposon screen for mutants defective in Actinomyces oris coaggregation with Streptococcus oralis. We obtained 33 independent clones, 13 of which completely failed to aggregate with S. oralis, and the remainder of which exhibited a range of phenotypes from severely to weakly defective coaggregation. The former had Tn5 insertions in fimA, cafA, or srtC2, as expected; the latter were mapped to genes coding for uncharacterized proteins and various nuo genes encoding the NADH dehydrogenase subunits. Electron microscopy and biochemical analyses of mutants with nonpolar deletions of nuo genes and ubiE, a menaquinone C-methyltransferase-encoding gene downstream of the nuo locus, confirmed the pilus and coaggregation defects. Both nuoA and ubiE mutants were defective in oxidation of MdbA, the major oxidoreductase required for oxidative folding of pilus proteins. Furthermore, supplementation of the ubiE mutant with exogenous menaquinone-4 rescued the cell growth and pilus defects. Altogether, we propose that the A. oris electron transport chain is biochemically linked to pilus assembly via oxidative protein folding. The Gram-positive actinobacterium A. oris expresses adhesive pili, or fimbriae, that are essential to biofilm formation and Actinomyces interactions with other bacteria, termed coaggregation. While the critical role of the conserved sortase machine in pilus assembly and the disulfide bond-forming catalyst MdbA in oxidative folding of pilins has been established, little is known about other trans-acting factors involved in these processes. Using a Tn5 transposon screen for mutants defective in coaggregation with Streptococcus oralis, we found that genetic disruption of the NADH dehydrogenase and menaquinone biosynthesis detrimentally alters pilus assembly. Further biochemical characterizations determined that menaquinone is important for reactivation of MdbA. This study supports the notion that the electron transport chain is biochemically linked to pilus assembly in A. oris via oxidative folding of pilin precursors.
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9
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Callegan MC, Parkunan SM, Randall CB, Coburn PS, Miller FC, LaGrow AL, Astley RA, Land C, Oh SY, Schneewind O. The role of pili in Bacillus cereus intraocular infection. Exp Eye Res 2017; 159:69-76. [PMID: 28336259 PMCID: PMC5492386 DOI: 10.1016/j.exer.2017.03.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 03/09/2017] [Accepted: 03/16/2017] [Indexed: 12/15/2022]
Abstract
Bacterial endophthalmitis is a potentially blinding intraocular infection. The bacterium Bacillus cereus causes a devastating form of this disease which progresses rapidly, resulting in significant inflammation and loss of vision within a few days. The outer surface of B. cereus incites the intraocular inflammatory response, likely through interactions with innate immune receptors such as TLRs. This study analyzed the role of B. cereus pili, adhesion appendages located on the bacterial surface, in experimental endophthalmitis. To test the hypothesis that the presence of pili contributed to intraocular inflammation and virulence, we analyzed the progress of experimental endophthalmitis in mouse eyes infected with wild type B. cereus (ATCC 14579) or its isogenic pilus-deficient mutant (ΔbcpA-srtD-bcpB or ΔPil). One hundred CFU were injected into the mid-vitreous of one eye of each mouse. Infections were analyzed by quantifying intraocular bacilli and retinal function loss, and by histology from 0 to 12 h postinfection. In vitro growth and hemolytic phenotypes of the infecting strains were also compared. There was no difference in hemolytic activity (1:8 titer), motility, or in vitro growth (p > 0.05, every 2 h, 0-18 h) between wild type B. cereus and the ΔPil mutant. However, infected eyes contained greater numbers of wild type B. cereus than ΔPil during the infection course (p ≤ 0.05, 3-12 h). Eyes infected with wild type B. cereus experienced greater losses in retinal function than eyes infected with the ΔPil mutant, but the differences were not always significant. Eyes infected with ΔPil or wild type B. cereus achieved similar degrees of severe inflammation. The results indicated that the intraocular growth of pilus-deficient B. cereus may have been better controlled, leading to a trend of greater retinal function in eyes infected with the pilus-deficient strain. Although this difference was not enough to significantly alter the severity of the inflammatory response, these results suggest a potential role for pili in protecting B. cereus from clearance during the early stages of endophthalmitis, which is a newly described virulence mechanism for this organism and this infection.
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Affiliation(s)
- Michelle C. Callegan
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA,Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, 950 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA,Dean A. McGee Eye Institute, Oklahoma City Oklahoma USA,Corresponding author: DMEI PA-418, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Phone: (405) 271-3674, Fax: (405) 271-8128,
| | - Salai Madhumathi Parkunan
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, 950 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - C. Blake Randall
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Phillip S. Coburn
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Frederick C. Miller
- Department of Cell Biology, University of Oklahoma Health Sciences Center, 950 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Austin L. LaGrow
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Roger A. Astley
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Craig Land
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - So-Young Oh
- Department of Microbiology, University of Chicago, 920 East 58
| | - Olaf Schneewind
- Department of Microbiology, University of Chicago, 920 East 58
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10
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Siegel SD, Liu J, Ton-That H. Biogenesis of the Gram-positive bacterial cell envelope. Curr Opin Microbiol 2016; 34:31-37. [PMID: 27497053 PMCID: PMC5164837 DOI: 10.1016/j.mib.2016.07.015] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Accepted: 07/19/2016] [Indexed: 01/29/2023]
Abstract
The Gram-positive cell envelope serves as a molecular platform for surface display of capsular polysaccharides, wall teichoic acids (WTAs), lipoteichoic acids (LTAs), lipoproteins, surface proteins and pili. WTAs, LTAs, and sortase-assembled pili are a few features that make the Gram-positive cell envelope distinct from the Gram-negative counterpart. Interestingly, a set of LytR-CpsA-Psr family proteins, found in all Gram-positives but limited to a minority of Gram-negative organisms, plays divergent functions, while decorating the cell envelope with glycans. Furthermore, a phylum of Gram-positive bacteria, the actinobacteria, appear to employ oxidative protein folding as the major folding mechanism, typically occurring in an oxidizing environment of the Gram-negative periplasm. These distinctive features will be highlighted, along with recent findings in the cell envelope biogenesis.
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Affiliation(s)
- Sara D Siegel
- Department of Microbiology & Molecular Genetics, University of Texas McGovern Medical School, Houston, TX, USA
| | - Jun Liu
- Department of Pathology & Laboratory Medicine, University of Texas McGovern Medical School, Houston, TX, USA
| | - Hung Ton-That
- Department of Microbiology & Molecular Genetics, University of Texas McGovern Medical School, Houston, TX, USA.
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11
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Si L, Li P, Liu X, Luo L. Chinese herb medicine against Sortase A catalyzed transformations, a key role in gram-positive bacterial infection progress. J Enzyme Inhib Med Chem 2016; 31:184-196. [PMID: 27162091 DOI: 10.1080/14756366.2016.1178639] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Many Gram-positive bacteria can anchor their surface proteins to the cell wall peptidoglycan covalently by a common mechanism with Sortase A (SrtA), thus escaping from the host's identification of immune cells. SrtA can complete this anchoring process by cleaving LPXTG motif conserved among these surface proteins and thus these proteins anchor on the cell wall. Moreover, those SrtA mutants lose this capability to anchor these relative proteins, with these bacteria no longer infectious. Therefore, SrtA inhibitors can be promising anti-infective agents to cure bacterial infections. Chinese herb medicines (CHMs) (chosen from Science Citation Index) have exhibited inhibition on SrtA of Gram-positive pathogens irreversibly or reversibly. In general, CHMs are likely to have important long-term impact as new antibacterial compounds and sought after by academia and the pharmaceutical industry. This review mainly focuses on SrtA inhibitors from CHMs and the potential inhibiting mechanism related to chemical structures of compounds in CHMs.
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Affiliation(s)
- Lifang Si
- a School of Bioscience & Bioengineering, South China University of Technology, Guangzhou University Town , Panyu , Guangzhou , China
| | - Pan Li
- a School of Bioscience & Bioengineering, South China University of Technology, Guangzhou University Town , Panyu , Guangzhou , China
| | - Xiong Liu
- a School of Bioscience & Bioengineering, South China University of Technology, Guangzhou University Town , Panyu , Guangzhou , China
| | - Lixin Luo
- a School of Bioscience & Bioengineering, South China University of Technology, Guangzhou University Town , Panyu , Guangzhou , China
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12
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Bradshaw WJ, Davies AH, Chambers CJ, Roberts AK, Shone CC, Acharya KR. Molecular features of the sortase enzyme family. FEBS J 2015; 282:2097-114. [PMID: 25845800 DOI: 10.1111/febs.13288] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Revised: 03/13/2015] [Accepted: 03/28/2015] [Indexed: 01/31/2023]
Abstract
Bacteria possess complex and varying cell walls with many surface exposed proteins. Sortases are responsible for the covalent attachment of specific proteins to the peptidoglycan of the cell wall of Gram-positive bacteria. Sortase A of Staphylococcus aureus, which is seen as the archetypal sortase, has been shown to be essential for pathogenesis and has therefore received much attention as a potential target for novel therapeutics. Being widely present in Gram-positive bacteria, it is likely that other Gram-positive pathogens also require sortases for their pathogenesis. Sortases have also been shown to be of significant use in a range of industrial applications. We review current knowledge of the sortase family in terms of their structures, functions and mechanisms and summarize work towards their use as antibacterial targets and microbiological tools.
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Affiliation(s)
- William J Bradshaw
- Department of Biology and Biochemistry, University of Bath, UK.,Public Health England, Porton Down, Salisbury, UK
| | | | - Christopher J Chambers
- Department of Biology and Biochemistry, University of Bath, UK.,Public Health England, Porton Down, Salisbury, UK
| | | | | | - K Ravi Acharya
- Department of Biology and Biochemistry, University of Bath, UK
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13
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Abstract
Pili of Gram-positive bacteria are unique structures on the bacterial surface, assembled from covalently linked polypeptide subunits. Pilus assembly proceeds by transpeptidation reactions catalyzed by sortases, followed by covalent anchoring of the filament in the peptidoglycan layer. Another distinctive property is the presence of intramolecular isopeptide bonds, conferring extraordinary chemical and mechanical stability to these elongated structures. Besides their function in cell adhesion and biofilm formation, this section discusses possible application of pilus constituents as vaccine components against Gram-positive pathogens.
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14
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Baer S, Nigro J, Madej MP, Nisbet RM, Suryadinata R, Coia G, Hong LPT, Adams TE, Williams CC, Nuttall SD. Comparison of alternative nucleophiles for Sortase A-mediated bioconjugation and application in neuronal cell labelling. Org Biomol Chem 2014; 12:2675-85. [PMID: 24643508 DOI: 10.1039/c3ob42325e] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The Sortase A (SrtA) enzyme from Staphylococcus aureus catalyses covalent attachment of protein substrates to pentaglycine cross-bridges in the Gram positive bacterial cell wall. In vitro SrtA-mediated protein ligation is now an important protein engineering tool for conjugation of substrates containing the LPXTGX peptide recognition sequence to oligo-glycine nucleophiles. In order to explore the use of alternative nucleophiles in this system, five different rhodamine-labelled compounds, with N-terminal nucleophilic amino acids, triglycine, glycine, and lysine, or N-terminal non-amino acid nucleophiles ethylenediamine and cadaverine, were synthesized. These compounds were tested for their relative abilities to function as nucleophiles in SrtA-mediated bioconjugation reactions. N-Terminal triglycine, glycine and ethylenediamine were all efficient in labelling a range of LPETGG containing recombinant antibody and scaffold proteins and peptides, while reduced activity was observed for the other nucleophiles across the range of proteins and peptides studied. Expansion of the range of available nucleophiles which can be utilised in SrtA-mediated bioconjugation expands the range of potential applications for this technology. As a demonstration of the utility of this system, SrtA coupling was used to conjugate the triglycine rhodamine-labelled nucleophile to the C-terminus of an Im7 scaffold protein displaying Aβ, a neurologically important peptide implicated in Alzheimer's disease. Purified, labelled protein showed Aβ-specific targeting to mammalian neuronal cells. Demonstration of targeting neuronal cells with a chimeric protein illustrates the power of this system, and suggests that SrtA-mediated direct cell-surface labelling and visualisation is an achievable goal.
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Affiliation(s)
- Samuel Baer
- CSIRO Materials Science and Engineering, 343 Royal Parade, Parkville, Victoria 3052, Australia.
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15
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van Leeuwen HC, Klychnikov OI, Menks MA, Kuijper EJ, Drijfhout JW, Hensbergen PJ. Clostridium difficile
sortase recognizes a (S/P)PXTG sequence motif and can accommodate diaminopimelic acid as a substrate for transpeptidation. FEBS Lett 2014; 588:4325-33. [DOI: 10.1016/j.febslet.2014.09.041] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 09/09/2014] [Accepted: 09/24/2014] [Indexed: 02/07/2023]
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16
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Hastie JL, Williams KB, Sepúlveda C, Houtman JC, Forest KT, Ellermeier CD. Evidence of a bacterial receptor for lysozyme: binding of lysozyme to the anti-σ factor RsiV controls activation of the ecf σ factor σV. PLoS Genet 2014; 10:e1004643. [PMID: 25275625 PMCID: PMC4183432 DOI: 10.1371/journal.pgen.1004643] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Accepted: 07/31/2014] [Indexed: 02/02/2023] Open
Abstract
σ factors endow RNA polymerase with promoter specificity in bacteria. Extra-Cytoplasmic Function (ECF) σ factors represent the largest and most diverse family of σ factors. Most ECF σ factors must be activated in response to an external signal. One mechanism of activation is the stepwise proteolytic destruction of an anti-σ factor via Regulated Intramembrane Proteolysis (RIP). In most cases, the site-1 protease required to initiate the RIP process directly senses the signal. Here we report a new mechanism in which the anti-σ factor rather than the site-1 protease is the sensor. We provide evidence suggesting that the anti-σ factor RsiV is the bacterial receptor for the innate immune defense enzyme, lysozyme. The site-1 cleavage site is similar to the recognition site of signal peptidase and cleavage at this site is required for σV activation in Bacillus subtilis. We reconstitute site-1 cleavage in vitro and demonstrate that it requires both signal peptidase and lysozyme. We demonstrate that the anti-σ factor RsiV directly binds to lysozyme and muramidase activity is not required for σV activation. We propose a model in which the binding of lysozyme to RsiV activates RsiV for signal peptidase cleavage at site-1, initiating proteolytic destruction of RsiV and activation of σV. This suggests a novel mechanism in which conformational change in a substrate controls the cleavage susceptibility for signal peptidase. Thus, unlike other ECF σ factors which require regulated intramembrane proteolysis for activation, the sensor for σV activation is not the site-1 protease but the anti-σ factor. All cells sense and respond to changes in their environments by transmitting information across the membrane. In bacteria, σ factors provide promoter specificity to RNA polymerase. Bacteria encode Extra-Cytoplasmic Function (ECF) σ factors, which often respond to extracellular signals. Activation of some ECF σ factors is controlled by stepwise proteolytic destruction of an anti-σ factor which is initiated by a site-1 protease. In most cases, the site-1 protease required to initiate the RIP process is thought to be the signal sensor. Here we report that the anti-σ factor RsiV, and not the site-1 protease, is the sensor for σV activation. Activation of the ECF σ factor σV is induced by lysozyme, an innate immune defense enzyme. We identify the site-1 protease as signal peptidase, which is required for general protein secretion. The anti-σ factor RsiV directly binds lysozyme. Binding of lysozyme to RsiV allows signal peptidase to cleave RsiV at site-1 and this leads to activation of σV. Thus, the anti-σ factor functions as a bacterial receptor for lysozyme. RsiV homologs from C. difficile and E. faecalis also bind lysozyme, suggesting they may utilize this receptor-ligand mechanism to control activation of σV to induce lysozyme resistance.
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Affiliation(s)
- Jessica L. Hastie
- Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Kyle B. Williams
- Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Carolina Sepúlveda
- Department of Bacteriology, University of Wisconsin Madison, Madison, Wisconsin, United States of America
| | - Jon C. Houtman
- Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Katrina T. Forest
- Department of Bacteriology, University of Wisconsin Madison, Madison, Wisconsin, United States of America
| | - Craig D. Ellermeier
- Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
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17
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Schneewind O, Missiakas D. Sec-secretion and sortase-mediated anchoring of proteins in Gram-positive bacteria. BIOCHIMICA ET BIOPHYSICA ACTA 2014; 1843:1687-97. [PMID: 24269844 PMCID: PMC4031296 DOI: 10.1016/j.bbamcr.2013.11.009] [Citation(s) in RCA: 92] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Revised: 11/01/2013] [Accepted: 11/13/2013] [Indexed: 01/17/2023]
Abstract
Signal peptide-driven secretion of precursor proteins directs polypeptides across the plasma membrane of bacteria. Two pathways, Sec- and SRP-dependent, converge at the SecYEG translocon to thread unfolded precursor proteins across the membrane, whereas folded preproteins are routed via the Tat secretion pathway. Gram-positive bacteria lack an outer membrane and are surrounded by a rigid layer of peptidoglycan. Interactions with their environment are mediated by proteins that are retained in the cell wall, often through covalent attachment to the peptidoglycan. In this review, we describe the mechanisms for both Sec-dependent secretion and sortase-dependent assembly of proteins in the envelope of Gram-positive bacteria. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.
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Affiliation(s)
- Olaf Schneewind
- Department of Microbiology, University of Chicago, Chicago, IL 60637, USA.
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18
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Douillard FP, Rasinkangas P, von Ossowski I, Reunanen J, Palva A, de Vos WM. Functional identification of conserved residues involved in Lactobacillus rhamnosus strain GG sortase specificity and pilus biogenesis. J Biol Chem 2014; 289:15764-75. [PMID: 24753244 DOI: 10.1074/jbc.m113.542332] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
In Gram-positive bacteria, sortase-dependent pili mediate the adhesion of bacteria to host epithelial cells and play a pivotal role in colonization, host signaling, and biofilm formation. Lactobacillus rhamnosus strain GG, a well known probiotic bacterium, also displays on its cell surface mucus-binding pilus structures, along with other LPXTG surface proteins, which are processed by sortases upon specific recognition of a highly conserved LPXTG motif. Bioinformatic analysis of all predicted LPXTG proteins encoded by the L. rhamnosus GG genome revealed a remarkable conservation of glycine residues juxtaposed to the canonical LPXTG motif. Here, we investigated and defined the role of this so-called triple glycine (TG) motif in determining sortase specificity during the pilus assembly and anchoring. Mutagenesis of the TG motif resulted in a lack or an alteration of the L. rhamnosus GG pilus structures, indicating that the TG motif is critical in pilus assembly and that they govern the pilin-specific and housekeeping sortase specificity. This allowed us to propose a regulatory model of the L. rhamnosus GG pilus biogenesis. Remarkably, the TG motif was identified in multiple pilus gene clusters of other Gram-positive bacteria, suggesting that similar signaling mechanisms occur in other, mainly pathogenic, species.
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Affiliation(s)
- François P Douillard
- From the Department of Veterinary Biosciences, University of Helsinki, Helsinki 00790, Finland and
| | - Pia Rasinkangas
- From the Department of Veterinary Biosciences, University of Helsinki, Helsinki 00790, Finland and
| | - Ingemar von Ossowski
- From the Department of Veterinary Biosciences, University of Helsinki, Helsinki 00790, Finland and
| | - Justus Reunanen
- From the Department of Veterinary Biosciences, University of Helsinki, Helsinki 00790, Finland and
| | - Airi Palva
- From the Department of Veterinary Biosciences, University of Helsinki, Helsinki 00790, Finland and
| | - Willem M de Vos
- From the Department of Veterinary Biosciences, University of Helsinki, Helsinki 00790, Finland and the Laboratory of Microbiology, Wageningen University, 6708 PB Wageningen, The Netherlands
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19
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Pilin and sortase residues critical for endocarditis- and biofilm-associated pilus biogenesis in Enterococcus faecalis. J Bacteriol 2013; 195:4484-95. [PMID: 23913319 DOI: 10.1128/jb.00451-13] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Enterococci commonly cause hospital-acquired infections, such as infective endocarditis and catheter-associated urinary tract infections. In animal models of these infections, a long hairlike extracellular protein fiber known as the endocarditis- and biofilm-associated (Ebp) pilus is an important virulence factor for Enterococcus faecalis. For Ebp and other sortase-assembled pili, the pilus-associated sortases are essential for fiber formation as they create covalent isopeptide bonds between the sortase recognition motif and the pilin-like motif of the pilus subunits. However, the molecular requirements governing the incorporation of the three pilus subunits (EbpA, EbpB, and EbpC) have not been investigated in E. faecalis. Here, we show that a Lys residue within the pilin-like motif of the EbpC subunit was necessary for EbpC polymerization. However, incorporation of EbpA into the pilus fiber only required its sortase recognition motif (LPXTG), while incorporation of EbpB only required its pilin-like motif. Only the sortase recognition motif would be required for incorporation of the pilus tip subunit, while incorporation of the base subunit would only require the pilin recognition motif. Thus, these data support a model with EbpA at the tip and EbpB at the base of an EbpC polymer. In addition, the housekeeping sortase, SrtA, was found to process EbpB and its predicted catalytic Cys residue was required for efficient cell wall anchoring of mature Ebp pili. Thus, we have defined molecular interactions involved in fiber polymerization, minor subunit organization, and pilus subcellular compartmentalization in the E. faecalis Ebp pilus system. These studies advance our understanding of unique molecular mechanisms of sortase-assembled pilus biogenesis.
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20
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Cozzi R, Zerbini F, Assfalg M, D'Onofrio M, Biagini M, Martinelli M, Nuccitelli A, Norais N, Telford JL, Maione D, Rinaudo CD. Group B Streptococcus pilus sortase regulation: a single mutation in the lid region induces pilin protein polymerization in vitro. FASEB J 2013; 27:3144-54. [PMID: 23631841 DOI: 10.1096/fj.13-227793] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Gram-positive bacteria build pili on their cell surface via a class C sortase-catalyzed transpeptidation mechanism from pilin protein substrates. Despite the availability of several crystal structures, pilus-related C sortases remain poorly characterized to date, and their mechanisms of transpeptidation and regulation need to be further investigated. The available 3-dimensional structures of these enzymes reveal a typical sortase fold, except for the presence of a unique feature represented by an N-terminal highly flexible loop known as the "lid." This region interacts with the residues composing the catalytic triad and covers the active site, thus maintaining the enzyme in an autoinhibited state and preventing the accessibility to the substrate. It is believed that enzyme activation may occur only after lid displacement from the catalytic domain. In this work, we provide the first direct evidence of the regulatory role of the lid, demonstrating that it is possible to obtain in vitro an efficient polymerization of pilin subunits using an active C sortase lid mutant carrying a single residue mutation in the lid region. Moreover, biochemical analyses of this recombinant mutant reveal that the lid confers thermodynamic and proteolytic stability to the enzyme.
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Affiliation(s)
- Roberta Cozzi
- Novartis Vaccines and Diagnostics, Via Fiorentina 1, 53100 Siena, Italy
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21
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Oxaran V, Ledue-Clier F, Dieye Y, Herry JM, Péchoux C, Meylheuc T, Briandet R, Juillard V, Piard JC. Pilus biogenesis in Lactococcus lactis: molecular characterization and role in aggregation and biofilm formation. PLoS One 2012; 7:e50989. [PMID: 23236417 PMCID: PMC3516528 DOI: 10.1371/journal.pone.0050989] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2012] [Accepted: 10/29/2012] [Indexed: 02/07/2023] Open
Abstract
The genome of Lactococcus lactis strain IL1403 harbors a putative pilus biogenesis cluster consisting of a sortase C gene flanked by 3 LPxTG protein encoding genes (yhgD, yhgE, and yhhB), called here pil. However, pili were not detected under standard growth conditions. Over-expression of the pil operon resulted in production and display of pili on the surface of lactococci. Functional analysis of the pilus biogenesis machinery indicated that the pilus shaft is formed by oligomers of the YhgE pilin, that the pilus cap is formed by the YhgD pilin and that YhhB is the basal pilin allowing the tethering of the pilus fibers to the cell wall. Oligomerization of pilin subunits was catalyzed by sortase C while anchoring of pili to the cell wall was mediated by sortase A. Piliated L. lactis cells exhibited an auto-aggregation phenotype in liquid cultures, which was attributed to the polymerization of major pilin, YhgE. The piliated lactococci formed thicker, more aerial biofilms compared to those produced by non-piliated bacteria. This phenotype was attributed to oligomers of YhgE. This study provides the first dissection of the pilus biogenesis machinery in a non-pathogenic Gram-positive bacterium. Analysis of natural lactococci isolates from clinical and vegetal environments showed pili production under standard growth conditions. The identification of functional pili in lactococci suggests that the changes they promote in aggregation and biofilm formation may be important for the natural lifestyle as well as for applications in which these bacteria are used.
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Affiliation(s)
- Virginie Oxaran
- INRA, UMR1319 Micalis, Domaine de Vilvert, Jouy-en-Josas, France
- Agro ParisTech, UMR 1319 Micalis, Jouy-en-Josas, France
| | - Florence Ledue-Clier
- INRA, UMR1319 Micalis, Domaine de Vilvert, Jouy-en-Josas, France
- Agro ParisTech, UMR 1319 Micalis, Jouy-en-Josas, France
| | - Yakhya Dieye
- INRA, UMR1319 Micalis, Domaine de Vilvert, Jouy-en-Josas, France
- Agro ParisTech, UMR 1319 Micalis, Jouy-en-Josas, France
| | - Jean-Marie Herry
- INRA, UMR1319 Micalis, Domaine de Vilvert, Jouy-en-Josas, France
- Agro ParisTech, UMR 1319 Micalis, Jouy-en-Josas, France
| | | | - Thierry Meylheuc
- INRA, UMR1319 Micalis, Domaine de Vilvert, Jouy-en-Josas, France
- Agro ParisTech, UMR 1319 Micalis, Jouy-en-Josas, France
| | - Romain Briandet
- INRA, UMR1319 Micalis, Domaine de Vilvert, Jouy-en-Josas, France
- Agro ParisTech, UMR 1319 Micalis, Jouy-en-Josas, France
| | - Vincent Juillard
- INRA, UMR1319 Micalis, Domaine de Vilvert, Jouy-en-Josas, France
- Agro ParisTech, UMR 1319 Micalis, Jouy-en-Josas, France
| | - Jean-Christophe Piard
- INRA, UMR1319 Micalis, Domaine de Vilvert, Jouy-en-Josas, France
- Agro ParisTech, UMR 1319 Micalis, Jouy-en-Josas, France
- * E-mail:
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22
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Robson SA, Jacobitz AW, Phillips ML, Clubb RT. Solution structure of the sortase required for efficient production of infectious Bacillus anthracis spores. Biochemistry 2012; 51:7953-63. [PMID: 22974341 DOI: 10.1021/bi300867t] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bacillus anthracis forms metabolically dormant endospores that upon germination can cause lethal anthrax disease in humans. Efficient sporulation requires the activity of the SrtC sortase (BaSrtC), a cysteine transpeptidase that covalently attaches the BasH and BasI proteins to the peptidoglycan of the forespore and predivisional cell, respectively. To gain insight into the molecular basis of protein display, we used nuclear magnetic resonance to determine the structure and backbone dynamics of the catalytic domain of BaSrtC (residues Ser(56)-Lys(198)). The backbone and heavy atom coordinates of structurally ordered amino acids have coordinate precision of 0.42 ± 0.07 and 0.82 ± 0.05 Å, respectively. BaSrtC(Δ55) adopts an eight-stranded β-barrel fold that contains two short helices positioned on opposite sides of the protein. Surprisingly, the protein dimerizes and contains an extensive, structurally disordered surface that is positioned adjacent to the active site. The surface is formed by two loops (β2-β3 and β4-H1 loops) that surround the active site histidine, suggesting that they may play a key role in associating BaSrtC with its lipid II substrate. BaSrtC anchors proteins bearing a noncanonical LPNTA sorting signal. Modeling studies suggest that the enzyme recognizes this substrate using a rigid binding pocket and reveals the presence of a conserved subsite for the signal. This first structure of a class D member of the sortase superfamily unveils class-specific features that may facilitate ongoing efforts to discover sortase inhibitors for the treatment of bacterial infections.
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Affiliation(s)
- Scott A Robson
- Department of Chemistry and Biochemistry, University of California, Los Angeles , 611 Charles Young Drive East, Los Angeles, California 90095, USA
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23
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Hendrickx APA, Poor CB, Jureller JE, Budzik JM, He C, Schneewind O. Isopeptide bonds of the major pilin protein BcpA influence pilus structure and bundle formation on the surface of Bacillus cereus. Mol Microbiol 2012; 85:152-63. [PMID: 22624947 DOI: 10.1111/j.1365-2958.2012.08098.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Bacillus cereus strains elaborate pili on their surface using a mechanism of sortase-mediated cross-linking of major and minor pilus components. Here we used a combination of electron microscopy and atomic force microscopy to visualize these structures. Pili occur as single, double or higher order assemblies of filaments formed from monomers of the major pilin, BcpA, capped by the minor pilin, BcpB. Previous studies demonstrated that within assembled pili, four domains of BcpA - CNA(1), CNA(2), XNA and CNA(3) - each acquire intramolecular lysine-asparagine isopeptide bonds formed via catalytic glutamic acid or aspartic acid residues. Here we showed that mutants unable to form the intramolecular isopeptide bonds in the CNA(2) or CNA(3) domains retain the ability to form pilus bundles. A mutant lacking the CNA(1) isopeptide bond assembled deformed pilin subunits that failed to associate as bundles. X-ray crystallography revealed that the BcpA variant Asp(312) Ala, lacking an aspartyl catalyst, did not generate the isopeptide bond within the jelly-roll structure of XNA. The Asp(312) Ala mutant was also unable to form bundles and promoted the assembly of deformed pili. Thus, structural integrity of the CNA(1) and XNA domains are determinants for the association of pili into higher order bundle structures and determine native pilus structure.
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24
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Schneewind O, Missiakas DM. Protein secretion and surface display in Gram-positive bacteria. Philos Trans R Soc Lond B Biol Sci 2012; 367:1123-39. [PMID: 22411983 PMCID: PMC3297441 DOI: 10.1098/rstb.2011.0210] [Citation(s) in RCA: 175] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The cell wall peptidoglycan of Gram-positive bacteria functions as a surface organelle for the transport and assembly of proteins that interact with the environment, in particular, the tissues of an infected host. Signal peptide-bearing precursor proteins are secreted across the plasma membrane of Gram-positive bacteria. Some precursors carry C-terminal sorting signals with unique sequence motifs that are cleaved by sortase enzymes and linked to the cell wall peptidoglycan of vegetative forms or spores. The sorting signals of pilin precursors are cleaved by pilus-specific sortases, which generate covalent bonds between proteins leading to the assembly of fimbrial structures. Other precursors harbour surface (S)-layer homology domains (SLH), which fold into a three-pronged spindle structure and bind secondary cell wall polysaccharides, thereby associating with the surface of specific Gram-positive microbes. Type VII secretion is a non-canonical secretion pathway for WXG100 family proteins in mycobacteria. Gram-positive bacteria also secrete WXG100 proteins and carry unique genes that either contribute to discrete steps in secretion or represent distinctive substrates for protein transport reactions.
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Affiliation(s)
- Olaf Schneewind
- Department of Microbiology, University of Chicago, 920 East 58th Street, Chicago, IL 60637, USA.
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25
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Harvey DJ. Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008. MASS SPECTROMETRY REVIEWS 2012; 31:183-311. [PMID: 21850673 DOI: 10.1002/mas.20333] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2010] [Revised: 01/04/2011] [Accepted: 01/04/2011] [Indexed: 05/31/2023]
Abstract
This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.
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Affiliation(s)
- David J Harvey
- Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK.
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26
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Becherelli M, Manetti AGO, Buccato S, Viciani E, Ciucchi L, Mollica G, Grandi G, Margarit I. The ancillary protein 1 of Streptococcus pyogenes FCT-1 pili mediates cell adhesion and biofilm formation through heterophilic as well as homophilic interactions. Mol Microbiol 2012; 83:1035-47. [PMID: 22320452 PMCID: PMC3490378 DOI: 10.1111/j.1365-2958.2012.07987.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Gram-positive pili are known to play a role in bacterial adhesion to epithelial cells and in the formation of biofilm microbial communities. In the present study we undertook the functional characterization of the pilus ancillary protein 1 (AP1_M6) from Streptococcus pyogenes isolates expressing the FCT-1 pilus variant, known to be strong biofilm formers. Cell binding and biofilm formation assays using S. pyogenes in-frame deletion mutants, Lactococcus expressing heterologous FCT-1 pili and purified recombinant AP1_M6, indicated that this pilin is a strong cell adhesin that is also involved in bacterial biofilm formation. Moreover, we show that AP1_M6 establishes homophilic interactions that mediate inter-bacterial contact, possibly promoting bacterial colonization of target epithelial cells in the form of three-dimensional microcolonies. Finally, AP1_M6 knockout mutants were less virulent in mice, indicating that this protein is also implicated in GAS systemic infection.
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Affiliation(s)
- Marco Becherelli
- Novartis Vaccines and Diagnostics, Via Fiorentina 1, Siena, Italy
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27
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Kobayashi K, Sudiarta IP, Kodama T, Fukushima T, Ara K, Ozaki K, Sekiguchi J. Identification and characterization of a novel polysaccharide deacetylase C (PdaC) from Bacillus subtilis. J Biol Chem 2012; 287:9765-9776. [PMID: 22277649 DOI: 10.1074/jbc.m111.329490] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Cell wall metabolism and cell wall modification are very important processes that bacteria use to adjust to various environmental conditions. One of the main modifications is deacetylation of peptidoglycan. The polysaccharide deacetylase homologue, Bacillus subtilis YjeA (renamed PdaC), was characterized and found to be a unique deacetylase. The pdaC deletion mutant was sensitive to lysozyme treatment, indicating that PdaC acts as a deacetylase. The purified recombinant and truncated PdaC from Escherichia coli deacetylated B. subtilis peptidoglycan and its polymer, (-GlcNAc-MurNAc[-L-Ala-D-Glu]-)(n). Surprisingly, RP-HPLC and ESI-MS/MS analyses showed that the enzyme deacetylates N-acetylmuramic acid (MurNAc) not GlcNAc from the polymer. Contrary to Streptococcus pneumoniae PgdA, which shows high amino acid sequence similarity with PdaC and is a zinc-dependent GlcNAc deacetylase toward peptidoglycan, there was less dependence on zinc ion for deacetylation of peptidoglycan by PdaC than other metal ions (Mn(2+), Mg(2+), Ca(2+)). The kinetic values of the activity toward B. subtilis peptidoglycan were K(m) = 4.8 mM and k(cat) = 0.32 s(-1). PdaC also deacetylated N-acetylglucosamine (GlcNAc) oligomers with a K(m) = 12.3 mM and k(cat) = 0.24 s(-1) toward GlcNAc(4). Therefore, PdaC has GlcNAc deacetylase activity toward GlcNAc oligomers and MurNAc deacetylase activity toward B. subtilis peptidoglycan.
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Affiliation(s)
- Kaori Kobayashi
- Interdisciplinary Graduate School of Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan
| | - I Putu Sudiarta
- Interdisciplinary Graduate School of Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan
| | - Takeko Kodama
- Biological Science Laboratories, Kao Corporation, 2606 Akabane, Ichikai, Haga, Tochigi 321-3497, Japan
| | - Tatsuya Fukushima
- Division of Gene Research, Department of Life Sciences, Research Center for Human and Environmental Sciences, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan and
| | - Katsutoshi Ara
- Biological Science Laboratories, Kao Corporation, 2606 Akabane, Ichikai, Haga, Tochigi 321-3497, Japan
| | - Katsuya Ozaki
- Biological Science Laboratories, Kao Corporation, 2606 Akabane, Ichikai, Haga, Tochigi 321-3497, Japan
| | - Junichi Sekiguchi
- Interdisciplinary Graduate School of Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan.
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28
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Abstract
In Gram-positive bacteria proteins are displayed on the cell surface using sortase enzymes. These cysteine transpeptidases join proteins bearing an appropriate sorting signal to strategically positioned amino groups on the cell surface. Working alone, or in concert with other enzymes, sortases either attach proteins to the cross-bridge peptide of the cell wall or they link proteins together to form pili. Because surface proteins play a fundamental role in microbial physiology and are frequently virulence factors, sortase enzymes have been intensely studied since their discovery a little more than a decade ago. Based on their primary sequences and functions sortases can be partitioned into distinct families called class A to F enzymes. Most bacteria elaborate their surfaces using more than one type of sortase that function non-redundantly by recognizing unique sorting signals within their protein substrates. Here we review what is known about the functions of these enzymes and the molecular basis of catalysis. Particular emphasis is placed on 'pilin' specific class C sortases that construct structurally complex pili. Exciting new data have revealed that these enzymes are amazingly promiscuous in the substrates that they can employ and that there is a startling degree of diversity in their mechanism of action. We also review recent data that suggest that sortases are targeted to specific sites on the cell surface where they work with other sortases and accessory factors to properly function.
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Affiliation(s)
- Thomas Spirig
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
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29
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Khare B, Krishnan V, Rajashankar KR, I-Hsiu H, Xin M, Ton-That H, Narayana SV. Structural differences between the Streptococcus agalactiae housekeeping and pilus-specific sortases: SrtA and SrtC1. PLoS One 2011; 6:e22995. [PMID: 21912586 PMCID: PMC3166054 DOI: 10.1371/journal.pone.0022995] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2011] [Accepted: 07/06/2011] [Indexed: 11/19/2022] Open
Abstract
The assembly of pili on the cell wall of Gram-positive bacteria requires transpeptidase enzymes called sortases. In Streptococcus agalactiae, the PI-1 pilus island of strain 2603V/R encodes two pilus-specific sortases (SrtC1 and SrtC2) and three pilins (GBS80, GBS52 and GBS104). Although either pilus-specific sortase is sufficient for the polymerization of the major pilin, GBS80, incorporation of the minor pilins GBS52 and GBS104 into the pilus structure requires SrtC1 and SrtC2, respectively. The S. agalactiae housekeeping sortase, SrtA, whose gene is present at a different location and does not catalyze pilus polymerization, was shown to be involved in cell wall anchoring of pilus polymers. To understand the structural basis of sortases involved in such diverse functions, we determined the crystal structures of S. agalactiae SrtC1 and SrtA. Both enzymes are made of an eight-stranded beta-barrel core with variations in their active site architecture. SrtA exhibits a catalytic triad arrangement similar to that in Streptococcus pyogenes SrtA but different from that in Staphylococcus aureus SrtA. In contrast, the SrtC1 enzyme contains an N-terminal helical domain and a ‘lid’ in its putative active site, which is similar to that seen in Streptococcus pneumoniae pilus-specific sortases, although with subtle differences in positioning and composition. To understand the effect of such differences on substrate recognition, we have also determined the crystal structure of a SrtC1 mutant, in which the conserved DP(W/F/Y) motif was replaced with the sorting signal motif of GBS80, IPNTG. By comparing the structures of WT wild type SrtA and SrtC1 and the ‘lid’ mutant of SrtC1, we propose that structural elements within the active site and the lid may be important for defining the role of specific sortase in pili biogenesis.
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Affiliation(s)
- B. Khare
- Center for Biophysical Sciences and Engineering, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - V. Krishnan
- Center for Biophysical Sciences and Engineering, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - K. R. Rajashankar
- NE-CAT, Advanced Photon Source, Argonne National Laboratory, Chicago, Illinois, United States of America
| | - H. I-Hsiu
- University of Texas Health Science Center, Houston, Texas, United States of America
| | - M. Xin
- University of Texas Health Science Center, Houston, Texas, United States of America
| | - H. Ton-That
- University of Texas Health Science Center, Houston, Texas, United States of America
| | - S. V. Narayana
- Center for Biophysical Sciences and Engineering, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
- * E-mail:
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30
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Anderson TD, Robson SA, Jiang XW, Malmirchegini GR, Fierobe HP, Lazazzera BA, Clubb RT. Assembly of minicellulosomes on the surface of Bacillus subtilis. Appl Environ Microbiol 2011; 77:4849-58. [PMID: 21622797 PMCID: PMC3147385 DOI: 10.1128/aem.02599-10] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2010] [Accepted: 05/13/2011] [Indexed: 11/20/2022] Open
Abstract
To cost-efficiently produce biofuels, new methods are needed to convert lignocellulosic biomass into fermentable sugars. One promising approach is to degrade biomass using cellulosomes, which are surface-displayed multicellulase-containing complexes present in cellulolytic Clostridium and Ruminococcus species. In this study we created cellulolytic strains of Bacillus subtilis that display one or more cellulase enzymes. Proteins containing the appropriate cell wall sorting signal are covalently anchored to the peptidoglycan by coexpressing them with the Bacillus anthracis sortase A (SrtA) transpeptidase. This approach was used to covalently attach the Cel8A endoglucanase from Clostridium thermocellum to the cell wall. In addition, a Cel8A-dockerin fusion protein was anchored on the surface of B. subtilis via noncovalent interactions with a cell wall-attached cohesin module. We also demonstrate that it is possible to assemble multienzyme complexes on the cell surface. A three-enzyme-containing minicellulosome was displayed on the cell surface; it consisted of a cell wall-attached scaffoldin protein noncovalently bound to three cellulase-dockerin fusion proteins that were produced in Escherichia coli. B. subtilis has a robust genetic system and is currently used in a wide range of industrial processes. Thus, grafting larger, more elaborate minicellulosomes onto the surface of B. subtilis may yield cellulolytic bacteria with increased potency that can be used to degrade biomass.
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Affiliation(s)
| | | | | | | | | | - Beth A. Lazazzera
- Molecular Biology Institute
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, 611 Charles E. Young Drive, Los Angeles, California 90095-1570
| | - Robert T. Clubb
- Department of Chemistry and Biochemistry
- UCLA-DOE Institute for Genomics and Proteomics
- Molecular Biology Institute
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31
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Popp MWL, Ploegh HL. Bilden und Brechen von Peptidbindungen: Protein-Engineering mithilfe von Sortase. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201008267] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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32
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Popp MWL, Ploegh HL. Making and breaking peptide bonds: protein engineering using sortase. Angew Chem Int Ed Engl 2011; 50:5024-32. [PMID: 21538739 DOI: 10.1002/anie.201008267] [Citation(s) in RCA: 221] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2010] [Indexed: 01/31/2023]
Abstract
Sortases are a class of bacterial enzymes that possess transpeptidase activity. It is their ability to site-specifically break a peptide bond and then reform a new bond with an incoming nucleophile that makes sortase an attractive tool for protein engineering. This technique has been adopted for a range of applications, from chemistry-based to cell biology and technology. In this Minireview we provide a brief overview of the biology of sortase enzymes and current applications in protein engineering. We identify areas that lend themselves to further innovation and that suggest new applications.
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33
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Hendrickx APA, Budzik JM, Oh SY, Schneewind O. Architects at the bacterial surface - sortases and the assembly of pili with isopeptide bonds. Nat Rev Microbiol 2011; 9:166-76. [PMID: 21326273 DOI: 10.1038/nrmicro2520] [Citation(s) in RCA: 195] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The cell wall envelope of Gram-positive bacteria can be thought of as a surface organelle for the assembly of macromolecular structures that enable the unique lifestyle of each microorganism. Sortases - enzymes that cleave the sorting signals of secreted proteins to form isopeptide (amide) bonds between the secreted proteins and peptidoglycan or polypeptides - function as the principal architects of the bacterial surface. Acting alone or with other sortase enzymes, sortase construction leads to the anchoring of surface proteins at specific sites in the envelope or to the assembly of pili, which are fibrous structures formed from many protein subunits. The catalysis of intermolecular isopeptide bonds between pilin subunits is intertwined with the assembly of intramolecular isopeptide bonds within pilin subunits. Together, these isopeptide bonds endow these sortase products with adhesive properties and resistance to host proteases.
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Affiliation(s)
- Antoni P A Hendrickx
- Department of Microbiology, University of Chicago, 920 East 58th Street, Chicago, Illinois 60637, USA
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34
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Weiner EM, Robson S, Marohn M, Clubb RT. The Sortase A enzyme that attaches proteins to the cell wall of Bacillus anthracis contains an unusual active site architecture. J Biol Chem 2010; 285:23433-43. [PMID: 20489200 PMCID: PMC2906334 DOI: 10.1074/jbc.m110.135434] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Revised: 05/14/2010] [Indexed: 11/06/2022] Open
Abstract
The pathogen Bacillus anthracis uses the Sortase A (SrtA) enzyme to anchor proteins to its cell wall envelope during vegetative growth. To gain insight into the mechanism of protein attachment to the cell wall in B. anthracis we investigated the structure, backbone dynamics, and function of SrtA. The NMR structure of SrtA has been determined with a backbone coordinate precision of 0.40 +/- 0.07 A. SrtA possesses several novel features not previously observed in sortase enzymes including the presence of a structurally ordered amino terminus positioned within the active site and in contact with catalytically essential histidine residue (His(126)). We propose that this appendage, in combination with a unique flexible active site loop, mediates the recognition of lipid II, the second substrate to which proteins are attached during the anchoring reaction. pK(a) measurements indicate that His(126) is uncharged at physiological pH compatible with the enzyme operating through a "reverse protonation" mechanism. Interestingly, NMR relaxation measurements and the results of a model building study suggest that SrtA recognizes the LPXTG sorting signal through a lock-in-key mechanism in contrast to the prototypical SrtA enzyme from Staphylococcus aureus.
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Affiliation(s)
| | - Scott Robson
- From the
Department of Chemistry and Biochemistry
| | | | - Robert T. Clubb
- From the
Department of Chemistry and Biochemistry
- UCLA-DOE Institute of Genomics and Proteomics, and
- Molecular Biology Institute, University of California, Los Angeles, California 90095-1570
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35
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Roles of minor pilin subunits Spy0125 and Spy0130 in the serotype M1 Streptococcus pyogenes strain SF370. J Bacteriol 2010; 192:4651-9. [PMID: 20639332 DOI: 10.1128/jb.00071-10] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Adhesive pili on the surface of the serotype M1 Streptococcus pyogenes strain SF370 are composed of a major backbone subunit (Spy0128) and two minor subunits (Spy0125 and Spy0130), joined covalently by a pilin polymerase (Spy0129). Previous studies using recombinant proteins showed that both minor subunits bind to human pharyngeal (Detroit) cells (A. G. Manetti et al., Mol. Microbiol. 64:968-983, 2007), suggesting both may act as pilus-presented adhesins. While confirming these binding properties, studies described here indicate that Spy0125 is the pilus-presented adhesin and that Spy0130 has a distinct role as a wall linker. Pili were localized predominantly to cell wall fractions of the wild-type S. pyogenes parent strain and a spy0125 deletion mutant. In contrast, they were found almost exclusively in culture supernatants in both spy0130 and srtA deletion mutants, indicating that the housekeeping sortase (SrtA) attaches pili to the cell wall by using Spy0130 as a linker protein. Adhesion assays with antisera specific for individual subunits showed that only anti-rSpy0125 serum inhibited adhesion of wild-type S. pyogenes to human keratinocytes and tonsil epithelium to a significant extent. Spy0125 was localized to the tip of pili, based on a combination of mutant analysis and liquid chromatography-tandem mass spectrometry analysis of purified pili. Assays comparing parent and mutant strains confirmed its role as the adhesin. Unexpectedly, apparent spontaneous cleavage of a labile, proline-rich (8 of 14 residues) sequence separating the N-terminal approximately 1/3 and C-terminal approximately 2/3 of Spy0125 leads to loss of the N-terminal region, but analysis of internal spy0125 deletion mutants confirmed that this has no significant effect on adhesion.
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36
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Hilleringmann M, Ringler P, Müller SA, De Angelis G, Rappuoli R, Ferlenghi I, Engel A. Molecular architecture of Streptococcus pneumoniae TIGR4 pili. EMBO J 2010; 28:3921-30. [PMID: 19942854 DOI: 10.1038/emboj.2009.360] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2009] [Accepted: 11/06/2009] [Indexed: 01/16/2023] Open
Abstract
Although the pili of Gram-positive bacteria are putative virulence factors, little is known about their structure. Here we describe the molecular architecture of pilus-1 of Streptococcus pneumoniae, which is a major cause of morbidity and mortality worldwide. One major (RrgB) and two minor components (RrgA and RrgC) assemble into the pilus. Results from TEM and scanning transmission EM show that the native pili are approximately 6 nm wide, flexible filaments that can be over 1 microm long. They are formed by a single string of RrgB monomers and have a polarity defined by nose-like protrusions. These protrusions correlate to the shape of monomeric RrgB-His, which like RrgA-His and RrgC-His has an elongated, multi-domain structure. RrgA and RrgC are only present at the opposite ends of the pilus shaft, compatible with their putative roles as adhesin and anchor to the cell wall surface, respectively. Our structural analyses provide the first direct experimental evidence that the native S. pneumoniae pilus shaft is composed exclusively of covalently linked monomeric RrgB subunits oriented head-to-tail.
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37
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Intramolecular amide bonds stabilize pili on the surface of bacilli. Proc Natl Acad Sci U S A 2009; 106:19992-7. [PMID: 19903875 DOI: 10.1073/pnas.0910887106] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Gram-positive bacteria elaborate pili and do so without the participation of folding chaperones or disulfide bond catalysts. Sortases, enzymes that cut pilin precursors, form covalent bonds that link pilin subunits and assemble pili on the bacterial surface. We determined the x-ray structure of BcpA, the major pilin subunit of Bacillus cereus. The BcpA precursor encompasses 2 Ig folds (CNA(2) and CNA(3)) and one jelly-roll domain (XNA) each of which synthesizes a single intramolecular amide bond. A fourth amide bond, derived from the Ig fold of CNA(1), is formed only after pilin subunits have been incorporated into pili. We report that the domains of pilin precursors have evolved to synthesize a discrete sequence of intramolecular amide bonds, thereby conferring structural stability and protease resistance to pili.
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38
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Acyl enzyme intermediates in sortase-catalyzed pilus morphogenesis in gram-positive bacteria. J Bacteriol 2009; 191:5603-12. [PMID: 19592583 DOI: 10.1128/jb.00627-09] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In gram-positive bacteria, covalently linked pilus polymers are assembled by a specific transpeptidase enzyme called pilus-specific sortase. This sortase is postulated to cleave the LPXTG motif of a pilin precursor between threonine and glycine and to form an acyl enzyme intermediate with the substrate. Pilus polymerization is believed to occur through the resolution of this intermediate upon specific nucleophilic attack by the conserved lysine located within the pilin motif of another pilin monomer, which joins two pilins with an isopeptide bond formed between threonine and lysine. Here, we present evidence for sortase reaction intermediates in Corynebacterium diphtheriae. We show that truncated SrtA mutants that are loosely bound to the cytoplasmic membrane form high-molecular-weight complexes with SpaA polymers secreted into the extracellular milieu. These complexes are not formed with SpaA pilin mutants that have alanine substitutions in place of threonine in the LPXTG motif or lysine in the pilin motif. The same phenotype is observed with alanine substitutions of either the conserved cysteine or histidine residue of SrtA known to be required for catalysis. Remarkably, the assembly of SpaA pili, or the formation of intermediates, is abolished with a SrtA mutant missing the membrane-anchoring domain. We infer that pilus polymerization involves the formation of covalent pilin-sortase intermediates, which occurs within a molecular platform on the exoplasmic face of the cytoplasmic membrane that brings together both sortase and its cognate substrates in close proximity to each other, likely surrounding a secretion apparatus. We present electron microscopic data in support of this picture.
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39
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Budzik JM, Oh SY, Schneewind O. Sortase D forms the covalent bond that links BcpB to the tip of Bacillus cereus pili. J Biol Chem 2009; 284:12989-97. [PMID: 19269972 PMCID: PMC2676031 DOI: 10.1074/jbc.m900927200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2009] [Revised: 03/05/2009] [Indexed: 11/06/2022] Open
Abstract
Bacillus cereus and other Gram-positive bacteria elaborate pili via a sortase D-catalyzed transpeptidation mechanism from major and minor pilin precursor substrates. After cleavage of the LPXTG sorting signal of the major pilin, BcpA, sortase D forms an amide bond between the C-terminal threonine and the amino group of lysine within the YPKN motif of another BcpA subunit. Pilus assembly terminates upon sortase A cleavage of the BcpA sorting signal, resulting in a covalent bond between BcpA and the cell wall cross-bridge. Here, we show that the IPNTG sorting signal of BcpB, the minor pilin, is cleaved by sortase D but not by sortase A. The C-terminal threonine of BcpB is amide-linked to the YPKN motif of BcpA, thereby positioning BcpB at the tip of pili. Thus, unique attributes of the sorting signals of minor pilins provide Gram-positive bacteria with a universal mechanism ordering assembly of pili.
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Affiliation(s)
- Jonathan M Budzik
- Department of Microbiology, University of Chicago, Chicago, IL 60637, USA
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40
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Quigley BR, Zähner D, Hatkoff M, Thanassi DG, Scott JR. Linkage of T3 and Cpa pilins in the Streptococcus pyogenes M3 pilus. Mol Microbiol 2009; 72:1379-94. [PMID: 19432798 DOI: 10.1111/j.1365-2958.2009.06727.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The important human pathogen Streptococcus pyogenes (group A streptococcus, GAS) initiates infection by pilus-mediated attachment to host tissue. Thus, the pilus is an excellent target for design of anti-infective strategies. The T3 pilus of GAS is composed of multiple covalently linked subunits of the T3 protein to which the two minor pilins, Cpa and OrfB, are covalently attached. Because the proteins of GAS pili do not contain either of the motifs required for pilus polymerization in other Gram-positive bacteria, we investigated the residues involved in their linkage. We show that linkage of Cpa to T3 by the sortase family transpeptidase SrtC2 requires the VPPTG motif in the cell wall-sorting signal of Cpa. We also demonstrate that K173 of T3 is required both for T3 polymerization and for attachment of Cpa to T3. Therefore, attachment of Cpa to K173 of a T3 subunit would block further addition of T3 subunits to this end of the growing pilus. This implies that Cpa is located exclusively at the pilus tip, a location supported by immunogold electron microscopy, and suggests that, as for well-studied pili on Gram-negative bacteria, the role of the pilus is to present the adhesin external to the bacterial capsule.
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Affiliation(s)
- Bernard R Quigley
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322, USA
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41
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Antos JM, Popp MWL, Ernst R, Chew GL, Spooner E, Ploegh HL. A straight path to circular proteins. J Biol Chem 2009; 284:16028-36. [PMID: 19359246 DOI: 10.1074/jbc.m901752200] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Folding and stability are parameters that control protein behavior. The possibility of conferring additional stability on proteins has implications for their use in vivo and for their structural analysis in the laboratory. Cyclic polypeptides ranging in size from 14 to 78 amino acids occur naturally and often show enhanced resistance toward denaturation and proteolysis when compared with their linear counterparts. Native chemical ligation and intein-based methods allow production of circular derivatives of larger proteins, resulting in improved stability and refolding properties. Here we show that circular proteins can be made reversibly with excellent efficiency by means of a sortase-catalyzed cyclization reaction, requiring only minimal modification of the protein to be circularized.
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Affiliation(s)
- John M Antos
- Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA
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