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Forrest S, Welch M. Arming the troops: Post-translational modification of extracellular bacterial proteins. Sci Prog 2020; 103:36850420964317. [PMID: 33148128 PMCID: PMC10450907 DOI: 10.1177/0036850420964317] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Protein secretion is almost universally employed by bacteria. Some proteins are retained on the cell surface, whereas others are released into the extracellular milieu, often playing a key role in virulence. In this review, we discuss the diverse types and potential functions of post-translational modifications (PTMs) occurring to extracellular bacterial proteins.
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Affiliation(s)
- Suzanne Forrest
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - Martin Welch
- Department of Biochemistry, University of Cambridge, Cambridge, UK
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2
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Quantitative Proteomics Uncovers the Interaction between a Virulence Factor and Mutanobactin Synthetases in Streptococcus mutans. mSphere 2019; 4:4/5/e00429-19. [PMID: 31554721 PMCID: PMC6763767 DOI: 10.1128/msphere.00429-19] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Streptococcus mutans is the major bacterium associated with dental caries. In order to thrive on the highly populated tooth surface and cause disease, S. mutans must be able to protect itself from hydrogen peroxide-producing commensal bacteria and compete effectively against the neighboring microbes. S. mutans produces mutacins, small antimicrobial peptides which help control the population of competing bacterial species. In addition, S. mutans produces a peptide called mutanobactin, which offers S. mutans protection against oxidative stress. Here, we uncover a new link between the putative glycosyltransferase SMU_833 and the mutanobactin-synthesizing protein complex through quantitative proteomic analysis and a tandem-affinity protein purification scheme. Furthermore, we show that SMU_833 mediates bacterial sensitivity to oxidative stress and bacterial ability to compete with commensal streptococci. This study has revealed a previously unknown association between SMU_833 and mutanobactin and demonstrated the importance of SMU_833 in the fitness of S. mutans. Streptococcus mutans, the primary etiological agent of tooth decay, has developed multiple adhesion and virulence factors which enable it to colonize and compete with other bacteria. The putative glycosyltransferase SMU_833 is important for the virulence of S. mutans by altering the biofilm matrix composition and cariogenicity. In this study, we further characterized the smu_833 mutant by evaluating its effects on bacterial fitness. Loss of SMU_833 led to extracellular DNA-dependent bacterial aggregation. In addition, the mutant was more susceptible to oxidative stress and less competitive against H2O2 producing oral streptococci. Quantitative proteomics analysis revealed that SMU_833 deficiency resulted in the significant downregulation of 10 proteins encoded by a biosynthetic gene cluster responsible for the production of mutanobactin, a compound produced by S. mutans which helps it survive oxidative stress. Tandem affinity purification demonstrated that SMU_833 interacts with the synthetic enzymes responsible for the production of mutanobactin. Similar to the smu_833 mutant, the deletion of the mutanobactin gene cluster rendered the mutant less competitive against H2O2-producing streptococci. Our studies revealed a new link between SMU_833 virulence and mutanobactin, suggesting that SMU_833 represents a new virulent target that can be used to develop potential anticaries therapeutics. IMPORTANCEStreptococcus mutans is the major bacterium associated with dental caries. In order to thrive on the highly populated tooth surface and cause disease, S. mutans must be able to protect itself from hydrogen peroxide-producing commensal bacteria and compete effectively against the neighboring microbes. S. mutans produces mutacins, small antimicrobial peptides which help control the population of competing bacterial species. In addition, S. mutans produces a peptide called mutanobactin, which offers S. mutans protection against oxidative stress. Here, we uncover a new link between the putative glycosyltransferase SMU_833 and the mutanobactin-synthesizing protein complex through quantitative proteomic analysis and a tandem-affinity protein purification scheme. Furthermore, we show that SMU_833 mediates bacterial sensitivity to oxidative stress and bacterial ability to compete with commensal streptococci. This study has revealed a previously unknown association between SMU_833 and mutanobactin and demonstrated the importance of SMU_833 in the fitness of S. mutans.
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3
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GtfA Interacting with GtfB is Required for PsrP Glycosylation in Streptococcus pneumoniae. Jundishapur J Microbiol 2018. [DOI: 10.5812/jjm.68982] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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4
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Ghazaei C, Line El Helou M. Beyond proteostasis: Roles of type I chaperonins in bacterial pathogenesis. J Med Microbiol 2018; 67:1203-1211. [PMID: 30074472 DOI: 10.1099/jmm.0.000811] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nearly all bacterial species express two or more chaperonin genes. Recent data indicate that type I chaperonins may be key players in bacterial infections. This is partly due to the well-known contribution of chaperonins in cellular proteostasis, the latter being compromised during bacterial host infection. In addition to their protein-folding activity, it has been revealed that certain chaperonins also exhibit moonlighting functions that can contribute in different ways to bacterial pathogenicity. Examples range from inducing adhesion molecules in Chlamydophila pneumoniae to supporting intracellular survival in Mycobacterium tuberculosis and Leishmania donovani, to inducing cytokines in Helicobacter pylori to promoting antimicrobial resistance in Escherichia coli, amongst others. This article provides a thorough reviews of our current understanding of the different mechanisms involving type I chaperonins during bacteria-host interactions, and suggests new areas to be explored and the potential of finding new targets for fighting bacterial infections.
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Affiliation(s)
- Ciamak Ghazaei
- 1Department of Microbiology, University of Mohaghegh Ardabili, Ardabil, Iran
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5
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Chen Y, Bensing BA, Seepersaud R, Mi W, Liao M, Jeffrey PD, Shajahan A, Sonon RN, Azadi P, Sullam PM, Rapoport TA. Unraveling the sequence of cytosolic reactions in the export of GspB adhesin from Streptococcus gordonii. J Biol Chem 2018; 293:5360-5373. [PMID: 29462788 DOI: 10.1074/jbc.ra117.000963] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Revised: 02/05/2018] [Indexed: 12/24/2022] Open
Abstract
Many pathogenic bacteria, including Streptococcus gordonii, possess a pathway for the cellular export of a single serine-rich-repeat protein that mediates the adhesion of bacteria to host cells and the extracellular matrix. This adhesin protein is O-glycosylated by several cytosolic glycosyltransferases and requires three accessory Sec proteins (Asp1-3) for export, but how the adhesin protein is processed for export is not well understood. Here, we report that the S. gordonii adhesin GspB is sequentially O-glycosylated by three enzymes (GtfA/B, Nss, and Gly) that attach N-acetylglucosamine and glucose to Ser/Thr residues. We also found that modified GspB is transferred from the last glycosyltransferase to the Asp1/2/3 complex. Crystal structures revealed that both Asp1 and Asp3 are related to carbohydrate-binding proteins, suggesting that they interact with carbohydrates and bind glycosylated adhesin, a notion that was supported by further analyses. We further observed that Asp1 also has an affinity for phospholipids, which is attenuated by Asp2. In summary, our findings support a model in which the GspB adhesin is sequentially glycosylated by GtfA/B, Nss, and Gly and then transferred to the Asp1/2/3 complex in which Asp1 mediates the interaction of the Asp1/2/3 complex with the lipid bilayer for targeting of matured GspB to the export machinery.
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Affiliation(s)
- Yu Chen
- From the Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115
| | - Barbara A Bensing
- the Department of Medicine, San Francisco Veteran Affairs Medical Center, University of California at San Francisco, San Francisco, California 94121
| | - Ravin Seepersaud
- the Department of Medicine, San Francisco Veteran Affairs Medical Center, University of California at San Francisco, San Francisco, California 94121
| | - Wei Mi
- From the Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115
| | - Maofu Liao
- From the Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115
| | - Philip D Jeffrey
- the Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544
| | - Asif Shajahan
- the Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602, and
| | - Roberto N Sonon
- the Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602, and
| | - Parastoo Azadi
- the Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602, and
| | - Paul M Sullam
- the Department of Medicine, San Francisco Veteran Affairs Medical Center, University of California at San Francisco, San Francisco, California 94121
| | - Tom A Rapoport
- From the Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, .,the Howard Hughes Medical Institute, Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115
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6
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Ma Y, Hao L, Ke H, Liang Z, Ma J, Liu Z, Li Y. LuxS/AI-2 in Streptococcus agalactiae reveals a key role in acid tolerance and virulence. Res Vet Sci 2017; 115:501-507. [PMID: 28858764 DOI: 10.1016/j.rvsc.2017.07.032] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 07/18/2017] [Accepted: 07/26/2017] [Indexed: 12/30/2022]
Abstract
LuxS-mediated autoinducer-2 (AI-2) directly or indirectly regulates important physiologic function in a variety of bacteria. We found a luxS homologue in the genome of Streptococcus agalactiae, an important pathogen of tilapia. To investigate the relationship between luxS/AI-2 and pathogenicity for tilapia, its bioluminescent activity, acid resistance, cell adherence, virulence, and regulation of virulence gene were evaluated. Compared with the wild-type strain, the bioluminescent activity lost in the luxS mutant, its resistance to acid (pH2.8) was significantly decreased 33.8 times, and furthermore, its adherence to the NGF-2 cell line was dramatically reduced 3 times in the mutant strain. The virulence of the mutant strain was decreased in the tilapia infection model, exogenous AI-2 molecule (7.4nM) and luxS gene complementation with plasmid could complement the deficiencies of function in the luxS mutant strain. These results showed that inactivation of luxS gene caused a significant decrease of bioluminance, acid resistance, cell adhesion, virulence to tilapia and transcription levels of many virulence genes in S. agalactiae. Expression of the known stress resistance factors DnaK and GroEL, relative regulator factors CovR/CovS and virulence factor cpsE verified above results. These findings suggest that luxS may be involved in the interruption of bacterial virulence and resistance to environmental factors.
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Affiliation(s)
- Yanping Ma
- Guangdong Provincial key Laboratory of Livestock Disease Prevention, Guangdong Open Laboratory of Veterinary Public Health, Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, PR China
| | - Le Hao
- Guangdong Provincial key Laboratory of Livestock Disease Prevention, Guangdong Open Laboratory of Veterinary Public Health, Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, PR China
| | - Hao Ke
- Guangdong Provincial key Laboratory of Livestock Disease Prevention, Guangdong Open Laboratory of Veterinary Public Health, Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, PR China
| | - Zhiling Liang
- Guangdong Provincial key Laboratory of Livestock Disease Prevention, Guangdong Open Laboratory of Veterinary Public Health, Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, PR China
| | - Jiangyao Ma
- Guangdong Provincial key Laboratory of Livestock Disease Prevention, Guangdong Open Laboratory of Veterinary Public Health, Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, PR China
| | - Zhenxing Liu
- Guangdong Provincial key Laboratory of Livestock Disease Prevention, Guangdong Open Laboratory of Veterinary Public Health, Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, PR China.
| | - Yugu Li
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China.
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7
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Zhu F, Zhang H, Yang T, Haslam SM, Dell A, Wu H. Engineering and Dissecting the Glycosylation Pathway of a Streptococcal Serine-rich Repeat Adhesin. J Biol Chem 2017; 291:27354-27363. [PMID: 28039332 PMCID: PMC5207161 DOI: 10.1074/jbc.m116.752998] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Revised: 11/11/2016] [Indexed: 11/24/2022] Open
Abstract
Serine-rich repeat glycoproteins (SRRPs) are conserved in Gram-positive bacteria. They are crucial for modulating biofilm formation and bacterial-host interactions. Glycosylation of SRRPs plays a pivotal role in the process; thus understanding the glycosyltransferases involved is key to identifying new therapeutic drug targets. The glycosylation of Fap1, an SRRP of Streptococcus parasanguinis, is mediated by a gene cluster consisting of six genes: gtf1, gtf2, gly, gtf3, dGT1, and galT2. Mature Fap1 glycan possesses the sequence of Rha1–3Glc1-(Glc1–3GlcNAc1)-2,6-Glc1–6GlcNAc. Gtf12, Gtf3, and dGT1 are responsible for the first four steps of the Fap1 glycosylation, catalyzing the transfer of GlcNAc, Glc, Glc, and GlcNAc residues to the protein backbone sequentially. The role of GalT2 and Gly in the Fap1 glycosylation is unknown. In the present study, we synthesized the fully modified Fap1 glycan in Escherichia coli by incorporating all six genes from the cluster. This study represents the first reconstitution of an exogenous stepwise O-glycosylation synthetic pathway in E. coli. In addition, we have determined that GalT2 mediates the fifth step of the Fap1 glycosylation by adding a rhamnose residue, and Gly mediates the final glycosylation step by transferring glucosyl residues. Furthermore, inactivation of each glycosyltransferase gene resulted in differentially impaired biofilms of S. parasanguinis, demonstrating the importance of Fap1 glycosylation in the biofilm formation. The Fap1 glycosylation system offers an excellent model to engineer glycans using different permutations of glycosyltransferases and to investigate biosynthetic pathways of SRRPs because SRRP genetic loci are highly conserved.
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Affiliation(s)
- Fan Zhu
- From the Departments of Pediatric Dentistry and.,Microbiology, University of Alabama at Birmingham, Schools of Dentistry and Medicine, Birmingham, Alabama 35244 and
| | - Hua Zhang
- From the Departments of Pediatric Dentistry and
| | - Tiandi Yang
- the Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Stuart M Haslam
- the Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Anne Dell
- the Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Hui Wu
- From the Departments of Pediatric Dentistry and .,Microbiology, University of Alabama at Birmingham, Schools of Dentistry and Medicine, Birmingham, Alabama 35244 and
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Zhang H, Zhou M, Yang T, Haslam SM, Dell A, Wu H. New Helical Binding Domain Mediates a Glycosyltransferase Activity of a Bifunctional Protein. J Biol Chem 2016; 291:22106-22117. [PMID: 27539847 PMCID: PMC5063993 DOI: 10.1074/jbc.m116.731695] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Indexed: 11/08/2022] Open
Abstract
Serine-rich repeat glycoproteins (SRRPs) conserved in streptococci and staphylococci are important for bacterial colonization and pathogenesis. Fap1, a well studied SRRP is a major surface constituent of Streptococcus parasanguinis and is required for bacterial adhesion and biofilm formation. Biogenesis of Fap1 is a multistep process that involves both glycosylation and secretion. A series of glycosyltransferases catalyze sequential glycosylation of Fap1. We have identified a unique hybrid protein dGT1 (dual glycosyltransferase 1) that contains two distinct domains. N-terminal DUF1792 is a novel GT-D-type glycosyltransferase, transferring Glc residues to Glc-GlcNAc-modified Fap1. C-terminal dGT1 (CgT) is predicted to possess a typical GT-A-type glycosyltransferase, however, the activity remains unknown. In this study, we determine that CgT is a distinct glycosyltransferase, transferring GlcNAc residues to Glc-Glc-GlcNAc-modified Fap1. A 2.4-Å x-ray crystal structure reveals that CgT has a unique binding domain consisting of three α helices in addition to a typical GT-A-type glycosyltransferase domain. The helical domain is crucial for the oligomerization of CgT. Structural and biochemical studies revealed that the helix domain is required for the protein-protein interaction and crucial for the glycosyltransferase activity of CgT in vitro and in vivo. As the helix domain presents a novel structural fold, we conclude that CgT represents a new member of GT-A-type glycosyltransferases.
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Affiliation(s)
- Hua Zhang
- From the Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294 and
| | - Meixian Zhou
- From the Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294 and
| | - Tiandi Yang
- the Department of Life Sciences, Imperial College London, London, SW7 2AZ, United Kingdom
| | - Stuart M Haslam
- the Department of Life Sciences, Imperial College London, London, SW7 2AZ, United Kingdom
| | - Anne Dell
- the Department of Life Sciences, Imperial College London, London, SW7 2AZ, United Kingdom
| | - Hui Wu
- From the Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294 and
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9
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Duan D, Scoffield JA, Zhou X, Wu H. Fine-tuned production of hydrogen peroxide promotes biofilm formation of Streptococcus parasanguinis by a pathogenic cohabitant Aggregatibacter actinomycetemcomitans. Environ Microbiol 2016; 18:4023-4036. [PMID: 27348605 DOI: 10.1111/1462-2920.13425] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Revised: 06/13/2016] [Accepted: 06/19/2016] [Indexed: 11/28/2022]
Abstract
Balanced bacterial biofilm communities help to maintain host health. Disturbance of such balance can lead to bacterial dysbiosis and pathogenesis. However, complex and dynamic bacterial interactions within the biofilm communities are poorly understood. In this study, we used a dual-species biofilm consisting of the periodontal pathogen Aggregatibacter actinomycetemcomitans, and a commensal Streptococcus parasanguinis to investigate bacterial interactions since the two organisms have been found to coexist during the development of localized aggressive periodontal disease. We report that A. actinomycetemcomitans promoted biofilm formation of S. parasanguinis in vitro and in vivo. Protein profiling of S. parasanguinis co-cultured with A. actinomycetemcomitans revealed a significant decrease in the protein level of pyruvate oxidase(PoxL), an enzyme required for the generation of hydrogen peroxide (H2 O2 ). Consistently, the H2 O2 concentration was concurrently decreased. However, the complete removal of H2 O2 impaired the biofilm formation. H2 O2 at a low concentration range regulated by A. actinomycetemcomitans enhanced the biofilm formation. These results demonstrate that A. actinomycetemcomitans promotes the S. parasanguinis biofilm formation through modulating the production of H2 O2 by fine-tuning the expression of poxL, indicating that H2 O2 functions as a signaling molecule. Taken together, this report revealed a previously unknown bacteria-bacteria interaction mechanism.
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Affiliation(s)
- Dingyu Duan
- Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.,State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, 610041, China
| | - Jessica A Scoffield
- Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, AL, 35294, USA
| | - Xuedong Zhou
- State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, 610041, China
| | - Hui Wu
- Departments of Pediatric Dentistry and Microbiology, Schools of Dentistry and Medicine, University of Alabama at Birmingham, Birmingham, AL, 35294, USA
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10
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Zhang Q, Nguyen T, McMichael M, Velu SE, Zou J, Zhou X, Wu H. New small-molecule inhibitors of dihydrofolate reductase inhibit Streptococcus mutans. Int J Antimicrob Agents 2015; 46:174-82. [PMID: 26022931 DOI: 10.1016/j.ijantimicag.2015.03.015] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Revised: 03/30/2015] [Accepted: 03/31/2015] [Indexed: 02/05/2023]
Abstract
Streptococcus mutans is a major aetiological agent of dental caries. Formation of biofilms is a key virulence factor of S. mutans. Drugs that inhibit S. mutans biofilms may have therapeutic potential. Dihydrofolate reductase (DHFR) plays a critical role in regulating the metabolism of folate. DHFR inhibitors are thus potent drugs and have been explored as anticancer and antimicrobial agents. In this study, a library of analogues based on a DHFR inhibitor, trimetrexate (TMQ), an FDA-approved drug, was screened and three new analogues that selectively inhibited S. mutans were identified. The most potent inhibitor had a 50% inhibitory concentration (IC50) of 454.0±10.2nM for the biofilm and 8.7±1.9nM for DHFR of S. mutans. In contrast, the IC50 of this compound for human DHFR was ca. 1000nM, a >100-fold decrease in its potency, demonstrating the high selectivity of the analogue. An analogue that exhibited the least potency for the S. mutans biofilm also had the lowest activity towards inhibiting S. mutans DHFR, further indicating that inhibition of biofilms is related to reduced DHFR activity. These data, along with docking of the most potent analogue to the modelled DHFR structure, suggested that the TMQ analogues indeed selectively inhibited S. mutans through targeting DHFR. These potent and selective small molecules are thus promising lead compounds to develop new effective therapeutics to prevent and treat dental caries.
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Affiliation(s)
- Qiong Zhang
- State Key Laboratory of Oral Diseases, Department of Pediatric Dentistry, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan 610041, PR China; Department of Pediatric Dentistry, University of Alabama at Birmingham School of Dentistry, Birmingham, AL 35294, USA
| | - Thao Nguyen
- Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Megan McMichael
- Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Sadanandan E Velu
- Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Jing Zou
- State Key Laboratory of Oral Diseases, Department of Pediatric Dentistry, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan 610041, PR China
| | - Xuedong Zhou
- State Key Laboratory of Oral Diseases, Department of Pediatric Dentistry, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan 610041, PR China
| | - Hui Wu
- Department of Pediatric Dentistry, University of Alabama at Birmingham School of Dentistry, Birmingham, AL 35294, USA.
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11
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A conserved domain is crucial for acceptor substrate binding in a family of glucosyltransferases. J Bacteriol 2014; 197:510-7. [PMID: 25404702 DOI: 10.1128/jb.02267-14] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Serine-rich repeat glycoproteins (SRRPs) are highly conserved in streptococci and staphylococci. Glycosylation of SRRPs is important for bacterial adhesion and pathogenesis. Streptococcus agalactiae is the leading cause of bacterial sepsis and meningitis among newborns. Srr2, an SRRP from S. agalactiae strain COH1, has been implicated in bacterial virulence. Four genes (gtfA, gtfB, gtfC, and gtfD) located downstream of srr2 share significant homology with genes involved in glycosylation of other SRRPs. We have shown previously that gtfA and gtfB encode two glycosyltransferases, GtfA and GtfB, that catalyze the transfer of GlcNAc residues to the Srr2 polypeptide. However, the function of other glycosyltransferases in glycosylation of Srr2 is unknown. In this study, we determined that GtfC catalyzed the direct transfer of glucosyl residues to Srr2-GlcNAc. The GtfC crystal structure was solved at 2.7 Å by molecular replacement. Structural analysis revealed a loop region at the N terminus as a putative acceptor substrate binding domain. Deletion of this domain rendered GtfC unable to bind to its substrate Srr2-GlcNAc, concurrently abolished the glycosyltransferase activity of GtfC, and also altered glycosylation of Srr2. Furthermore, deletion of the corresponding regions from GtfC homologs also abolished their substrate binding and enzymatic activity, indicating that this region is functionally conserved. In summary, we have determined that GtfC is important for the glycosylation of Srr2 and identified a conserved loop region that is crucial for acceptor substrate binding from GtfC homologs in streptococci. These findings shed new mechanistic insight into this family of glycosyltransferases.
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12
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Modification of Streptococcus mutans Cnm by PgfS contributes to adhesion, endothelial cell invasion, and virulence. J Bacteriol 2014; 196:2789-97. [PMID: 24837294 DOI: 10.1128/jb.01783-14] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Expression of the surface protein Cnm has been directly implicated in the ability of certain strains of Streptococcus mutans to bind to collagen and to invade human coronary artery endothelial cells (HCAEC) and in the killing of Galleria mellonella. Sequencing analysis of Cnm(+) strains revealed that cnm is located between the core genes SMU.2067 and SMU.2069. Reverse transcription-PCR (RT-PCR) analysis showed that cnm is cotranscribed with SMU.2067, encoding a putative glycosyltransferase referred to here as PgfS (protein glycosyltransferase of streptococci). Notably, Cnm contains a threonine-rich domain predicted to undergo O-linked glycosylation. The previously shown abnormal migration pattern of Cnm, the presence of the threonine-rich domain, and the molecular linkage of cnm with pgfS lead us to hypothesize that PgfS modifies Cnm. A ΔpgfS strain showed defects in several traits associated with Cnm expression, including collagen binding, HCAEC invasion, and killing of G. mellonella. Western blot analysis revealed that Cnm from the ΔpgfS mutant migrated at a lower molecular weight than that from the parent strain. In addition, Cnm produced by ΔpgfS was highly susceptible to proteinase K degradation, in contrast to the high-molecular-weight Cnm version found in the parent strain. Lectin-binding analyses confirmed the glycosylated nature of Cnm and strongly suggested the presence of N-acetylglucosamine residues attached to Cnm. Based on these findings, the phenotypes observed in ΔpgfS are most likely associated with defects in Cnm glycosylation that affects protein function, stability, or both. In conclusion, this study demonstrates that Cnm is a glycoprotein and that posttranslational modification mediated by PgfS contributes to the virulence-associated phenotypes linked to Cnm.
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Bensing BA, Seepersaud R, Yen YT, Sullam PM. Selective transport by SecA2: an expanding family of customized motor proteins. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1843:1674-86. [PMID: 24184206 DOI: 10.1016/j.bbamcr.2013.10.019] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Revised: 10/20/2013] [Accepted: 10/23/2013] [Indexed: 01/22/2023]
Abstract
The SecA2 proteins are a special class of transport-associated ATPases that are related to the SecA component of the general Sec system, and are found in an increasingly large number of Gram-positive bacterial species. The SecA2 substrates are typically linked to the cell wall, but may be lipid-linked, peptidoglycan-linked, or non-covalently associated S-layer proteins. These substrates can have a significant impact on virulence of pathogenic organisms, but may also aid colonization by commensals. The SecA2 orthologues range from being highly similar to their SecA paralogues, to being distinctly different in apparent structure and function. Two broad classes of SecA2 are evident. One transports multiple substrates, and may interact with the general Sec system, or with an as yet unidentified transmembrane channel. The second type transports a single substrate, and is a component of the accessory Sec system, which includes the SecY paralogue SecY2 along with the accessory Sec proteins Asp1-3. Recent studies indicate that the latter three proteins may have a unique role in coordinating post-translational modification of the substrate with transport by SecA2. Comparative functional and phylogenetic analyses suggest that each SecA2 may be uniquely adapted for a specific type of substrate. 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)
- Barbara A Bensing
- San Francisco Veterans Affairs Medical Center and the University of California, San Francisco, CA 94121, USA.
| | - Ravin Seepersaud
- San Francisco Veterans Affairs Medical Center and the University of California, San Francisco, CA 94121, USA
| | - Yihfen T Yen
- San Francisco Veterans Affairs Medical Center and the University of California, San Francisco, CA 94121, USA
| | - Paul M Sullam
- San Francisco Veterans Affairs Medical Center and the University of California, San Francisco, CA 94121, USA
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Garnett JA, Matthews S. Interactions in bacterial biofilm development: a structural perspective. Curr Protein Pept Sci 2013; 13:739-55. [PMID: 23305361 PMCID: PMC3601411 DOI: 10.2174/138920312804871166] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Revised: 07/16/2012] [Accepted: 08/03/2012] [Indexed: 11/24/2022]
Abstract
A community-based life style is the normal mode of growth and survival for many bacterial species. These cellular accretions or biofilms are initiated upon recognition of solid phases by cell surface exposed adhesive moieties. Further cell-cell interactions, cell signalling and bacterial replication leads to the establishment of dense populations encapsulated in a mainly self-produced extracellular matrix; this comprises a complex mixture of macromolecules. These fascinating architectures protect the inhabitants from radiation damage, dehydration, pH fluctuations and antimicrobial compounds. As such they can cause bacterial persistence in disease and problems in industrial applications. In this review we discuss the current understandings of these initial biofilm-forming processes based on structural data. We also briefly describe latter biofilm maturation and dispersal events, which although lack high-resolution insights, are the present focus for many structural biologists working in this field. Finally we give an overview of modern techniques aimed at preventing and disrupting problem biofilms.
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Affiliation(s)
- James A Garnett
- Centre for Structural Biology, Department of Life Sciences, Imperial College London, South Kensington, London SW7 2AZ, UK
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15
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Iwashkiw JA, Vozza NF, Kinsella RL, Feldman MF. Pour some sugar on it: the expanding world of bacterial proteinO-linked glycosylation. Mol Microbiol 2013; 89:14-28. [DOI: 10.1111/mmi.12265] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/15/2013] [Indexed: 11/26/2022]
Affiliation(s)
- Jeremy A. Iwashkiw
- Alberta Glycomics Centre; Department of Biological Sciences; University of Alberta; CW405 Biological Sciences Building; Edmonton; Alberta; Canada; T6G 2E9
| | - Nicolas F. Vozza
- Alberta Glycomics Centre; Department of Biological Sciences; University of Alberta; CW405 Biological Sciences Building; Edmonton; Alberta; Canada; T6G 2E9
| | - Rachel L. Kinsella
- Alberta Glycomics Centre; Department of Biological Sciences; University of Alberta; CW405 Biological Sciences Building; Edmonton; Alberta; Canada; T6G 2E9
| | - Mario F. Feldman
- Alberta Glycomics Centre; Department of Biological Sciences; University of Alberta; CW405 Biological Sciences Building; Edmonton; Alberta; Canada; T6G 2E9
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16
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Gap2 promotes the formation of a stable protein complex required for mature Fap1 biogenesis. J Bacteriol 2013; 195:2166-76. [PMID: 23475979 DOI: 10.1128/jb.02255-12] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Serine-rich repeat glycoproteins (SRRPs) are important bacterial adhesins conserved in streptococci and staphylococci. Fap1, a SRRP identified in Streptococcus parasanguinis, is the major constituent of bacterial fimbriae and is required for adhesion and biofilm formation. An 11-gene cluster is required for Fap1 glycosylation and secretion; however, the exact mechanism of Fap1 biogenesis remains a mystery. Two glycosylation-associated proteins within this cluster--Gap1 and Gap3--function together in Fap1 biogenesis. Here we report the role of the third glycosylation-associated protein, Gap2. A gap2 mutant exhibited the same phenotype as the gap1 and gap3 mutants in terms of Fap1 biogenesis, fimbrial assembly, and bacterial adhesion, suggesting that the three proteins interact. Indeed, all three proteins interacted with each other independently and together to form a stable protein complex. Mechanistically, Gap2 protected Gap3 from degradation by ClpP protease, and Gap2 required the presence of Gap1 for expression at the wild-type level. Gap2 augmented the function of Gap1 in stabilizing Gap3; this function was conserved in Gap homologs from Streptococcus agalactiae. Our studies demonstrate that the three Gap proteins work in concert in Fap1 biogenesis and reveal a new function of Gap2. This insight will help us elucidate the molecular mechanism of SRRP biogenesis in this bacterium and in pathogenic species.
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17
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Differential localization of the streptococcal accessory sec components and implications for substrate export. J Bacteriol 2012. [PMID: 23204472 DOI: 10.1128/jb.01742-12] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The accessory Sec system of Streptococcus gordonii is comprised of SecY2, SecA2, and five proteins (Asp1 through -5) that are required for the export of a serine-rich glycoprotein, GspB. We have previously shown that a number of the Asps interact with GspB, SecA2, or each other. To further define the roles of these Asps in export, we examined their subcellular localization in S. gordonii and in Escherichia coli expressing the streptococcal accessory Sec system. In particular, we assessed how the locations of these accessory Sec proteins were altered by the presence of other components. Using fluorescence microscopy, we found in E. coli that SecA2 localized within multiple foci at the cell membrane, regardless of whether other accessory Sec proteins were expressed. Asp2 alone localized to the cell poles but formed a similar punctate pattern at the membrane when SecA2 was present. Asp1 and Asp3 localized diffusely in the cytosol when expressed alone or with SecA2. However, these proteins redistributed to the membrane in a punctate arrangement when all of the accessory Sec components were present. Cell fractionation studies with S. gordonii further corroborated these microscopy results. Collectively, these findings indicate that Asp1 to -3 are not integral membrane proteins that form structural parts of the translocation channel. Instead, SecA2 serves as a docking site for Asp2, which in turn attracts a complex of Asp1 and Asp3 to the membrane. These protein interactions may be important for the trafficking of GspB to the cell membrane and its subsequent translocation.
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18
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Abstract
The conserved general secretion (Sec) pathway carries out most protein export in bacteria and is powered by the essential ATPase SecA. Interestingly, mycobacteria and some Gram-positive bacteria possess two SecA proteins: SecA1 and SecA2. In these species, SecA1 is responsible for exporting most proteins, whereas SecA2 exports only a subset of substrates and is implicated in virulence. However, despite the impressive body of knowledge about the canonical SecA1, less is known concerning SecA2 function. Here, we review our current understanding of the different types of SecA2 systems and outline future directions for their study.
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Affiliation(s)
- Meghan E Feltcher
- Department of Microbiology and Immunology, School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-27290, USA
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19
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Lizcano A, Sanchez CJ, Orihuela CJ. A role for glycosylated serine-rich repeat proteins in gram-positive bacterial pathogenesis. Mol Oral Microbiol 2012; 27:257-69. [PMID: 22759311 DOI: 10.1111/j.2041-1014.2012.00653.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Bacterial attachment to host surfaces is a pivotal event in the biological and infectious processes of both commensal and pathogenic bacteria, respectively. Serine-rich repeat proteins (SRRPs) are a family of adhesins in Gram-positive bacteria that mediate attachment to a variety of host and bacterial surfaces. As such, they contribute towards a wide-range of diseases including sub-acute bacterial endocarditis, community-acquired pneumonia, and meningitis. SRRPs are unique in that they are glycosylated, require a non-canonical Sec-translocase for transport, and are largely composed of a domain containing hundreds of alternating serine residues. These serine-rich repeats are thought to extend a unique non-repeat (NR) domain outward away from the bacterial surface to mediate adhesion. So far, NR domains have been determined to bind to sialic acid moieties, keratins, or other NR domains of a similar SRRP. This review summarizes how this important family of bacterial adhesins mediates bacterial attachment to host and bacterial cells, contributes to disease pathogenesis, and might be targeted for pharmacological intervention or used as novel protective vaccine antigens. This review also highlights recent structural findings on the NR domains of these proteins.
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Affiliation(s)
- A Lizcano
- Department of Microbiology and Immunology, The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229-3900, USA
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