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Arenas T, Osorio A, Ginez LD, Camarena L, Poggio S. Bacterial cell-wall quantification by a modified low volume Nelson-Somogyi method and its use with different sugars. Can J Microbiol 2022; 68:295-302. [PMID: 35100051 DOI: 10.1139/cjm-2021-0238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The study of peptidoglycan binding proteins frequently requires in vitro binding assays in which the isolated peptidoglycan used as substrate has to be carefully quantified. Here we describe an easy and sensitive assay for the quantification of peptidoglycan based on a modified Nelson-Somogyi reducing sugar assay. We report the response of this assay to different common sugars and adapt its use to peptidoglycan samples that have been subjected to acid hydrolysis. This method showed a better sensitivity than the peptidoglycan quantification method based on the acid detection of diaminopimelic acid. The method described in this work besides being valuable in the characterization of peptidoglycan binding proteins, is also useful for quantification of reducing monosaccharides or of polysaccharides after acid or hydrolysis.
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Affiliation(s)
- Thelma Arenas
- Universidad Nacional Autónoma de México, 7180, Depto. Biología Molecular y Biotecnología, Ciudad de Mexico, Mexico;
| | - Aurora Osorio
- Universidad Nacional Autónoma de México, 7180, Depto. Biología Molecular y Biotecnología, Ciudad de Mexico, Mexico;
| | - Luis David Ginez
- National Autonomous University of Mexico, 7180, Molecular Biology and Biotechnology, Ciudad de Mexico, Mexico, 04510;
| | - Laura Camarena
- Universidad Nacional Autonoma de Mexico, 7180, Instituto de Investigaciones Biomédicas, Ciudad de Mexico, Ciudad de México, Mexico;
| | - Sebastian Poggio
- Universidad Nacional Autonoma de Mexico Instituto de Investigaciones Biomedicas, 61738, Biologia Molecular y Biotecnologia, Ciudad de Mexico, Ciudad de Mexico, Mexico;
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Dik DA, Marous DR, Fisher JF, Mobashery S. Lytic transglycosylases: concinnity in concision of the bacterial cell wall. Crit Rev Biochem Mol Biol 2017. [PMID: 28644060 DOI: 10.1080/10409238.2017.1337705] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The lytic transglycosylases (LTs) are bacterial enzymes that catalyze the non-hydrolytic cleavage of the peptidoglycan structures of the bacterial cell wall. They are not catalysts of glycan synthesis as might be surmised from their name. Notwithstanding the seemingly mundane reaction catalyzed by the LTs, their lytic reactions serve bacteria for a series of astonishingly diverse purposes. These purposes include cell-wall synthesis, remodeling, and degradation; for the detection of cell-wall-acting antibiotics; for the expression of the mechanism of cell-wall-acting antibiotics; for the insertion of secretion systems and flagellar assemblies into the cell wall; as a virulence mechanism during infection by certain Gram-negative bacteria; and in the sporulation and germination of Gram-positive spores. Significant advances in the mechanistic understanding of each of these processes have coincided with the successive discovery of new LTs structures. In this review, we provide a systematic perspective on what is known on the structure-function correlations for the LTs, while simultaneously identifying numerous opportunities for the future study of these enigmatic enzymes.
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Affiliation(s)
- David A Dik
- a Department of Chemistry and Biochemistry , University of Notre Dame , Notre Dame , IN , USA
| | - Daniel R Marous
- a Department of Chemistry and Biochemistry , University of Notre Dame , Notre Dame , IN , USA
| | - Jed F Fisher
- a Department of Chemistry and Biochemistry , University of Notre Dame , Notre Dame , IN , USA
| | - Shahriar Mobashery
- a Department of Chemistry and Biochemistry , University of Notre Dame , Notre Dame , IN , USA
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Domínguez-Gil T, Molina R, Alcorlo M, Hermoso JA. Renew or die: The molecular mechanisms of peptidoglycan recycling and antibiotic resistance in Gram-negative pathogens. Drug Resist Updat 2016; 28:91-104. [PMID: 27620957 DOI: 10.1016/j.drup.2016.07.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Antimicrobial resistance is one of the most serious health threats. Cell-wall remodeling processes are tightly regulated to warrant bacterial survival and in some cases are directly linked to antibiotic resistance. Remodeling produces cell-wall fragments that are recycled but can also act as messengers for bacterial communication, as effector molecules in immune response and as signaling molecules triggering antibiotic resistance. This review is intended to provide state-of-the-art information about the molecular mechanisms governing this process and gather structural information of the different macromolecular machineries involved in peptidoglycan recycling in Gram-negative bacteria. The growing body of literature on the 3D structures of the corresponding macromolecules reveals an extraordinary complexity. Considering the increasing incidence and widespread emergence of Gram-negative multidrug-resistant pathogens in clinics, structural information on the main actors of the recycling process paves the way for designing novel antibiotics disrupting cellular communication in the recycling-resistance pathway.
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Affiliation(s)
- Teresa Domínguez-Gil
- Department of Crystallography and Structural Biology, Inst. Química-Física "Rocasolano", CSIC, Serrano 119, 28006 Madrid, Spain
| | - Rafael Molina
- Department of Crystallography and Structural Biology, Inst. Química-Física "Rocasolano", CSIC, Serrano 119, 28006 Madrid, Spain
| | - Martín Alcorlo
- Department of Crystallography and Structural Biology, Inst. Química-Física "Rocasolano", CSIC, Serrano 119, 28006 Madrid, Spain
| | - Juan A Hermoso
- Department of Crystallography and Structural Biology, Inst. Química-Física "Rocasolano", CSIC, Serrano 119, 28006 Madrid, Spain.
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Herlihey FA, Moynihan PJ, Clarke AJ. The essential protein for bacterial flagella formation FlgJ functions as a β-N-acetylglucosaminidase. J Biol Chem 2014; 289:31029-42. [PMID: 25248745 DOI: 10.1074/jbc.m114.603944] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The flagellum is a major virulence factor of motile pathogenic bacteria. This structure requires more than 50 proteins for its biogenesis and function, one of which is FlgJ. Homologs of FlgJ produced by the β- and γ-proteobacteria, such as Salmonella enterica, Vibrio spp., and both Sphingomonas sp. and Pseudomonas spp. are bifunctional, possessing an N-terminal domain responsible for proper rod assembly and a C-terminal domain possessing peptidoglycan lytic activity. Despite the amount of research conducted on FlgJ from these and other bacteria over the past 15 years, no biochemical analysis had been conducted on any FlgJ and consequently confusion exists as to whether the enzyme is a peptidoglycan hydrolase or a lytic transglycosylase. In this study, we present the development of a novel assay for glycoside lytic enzymes and its use to provide the first enzymatic characterization of the lytic domain of FlgJ from S. enterica as the model enzyme. Surprisingly, FlgJ functions as neither a muramidase nor a lytic transglycosylases but rather as a β-N-acetylglucosaminidase. As such, FlgJ represents the first autolysin with this activity to be characterized from a Gram-negative bacterium. At its optimal pH of 4.0, the Michaelis-Menten parameters of K(m) and k(cat) for FlgJ from S. enterica were determined to be 0.64 ± 0.18 mg ml(-1) and 0.13 ± 0.016 s(-1), respectively, using purified PG as substrate. Its catalytic residues were identified as Glu(184) and Glu(223).
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Affiliation(s)
- Francesca A Herlihey
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Patrick J Moynihan
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Anthony J Clarke
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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5
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Meng F, Liu X, Wang Q. Identification of Wood Decay Related Genes fromPiptoporus Betulinus(Bull. Fr.) Karsten Using Differential Display Reverse Transcription PCR (DDRT-PCR). BIOTECHNOL BIOTEC EQ 2014. [DOI: 10.5504/bbeq.2012.0032] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Zhong Q, Zhao Y, Chen T, Yin S, Yao X, Wang J, Lu S, Tan Y, Tang J, Zheng B, Hu F, Li M. A functional peptidoglycan hydrolase characterized from T4SS in 89K pathogenicity island of epidemic Streptococcus suis serotype 2. BMC Microbiol 2014; 14:73. [PMID: 24655418 PMCID: PMC3974602 DOI: 10.1186/1471-2180-14-73] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Accepted: 03/20/2014] [Indexed: 12/29/2022] Open
Abstract
BACKGROUND Streptococcus suis serotype 2 (S. suis 2) has evolved efficient mechanisms to cause streptococcal toxic shock syndrome (STSS), which is a new emerging infectious disease linked to S. suis. We have previously reported that a type IV secretion system (T4SS) harbored by the specific 89K pathogenicity island (PAI) of S. suis 2 contributes to the development of STSS and mediates horizontal transfer of 89K. However, the 89K T4SS machinery assembly in vivo and in vitro is poorly understood, and the component acting directly to digest the bacterial cell wall needs to be identified. RESULTS The virB1-89K gene product encoded in the 89K PAI is the only one that shows similarity to the Agrobacterium VirB1 component and contains a conserved CHAP domain that may function in peptidoglycan hydrolysis, which makes it a plausible candidate acting as a hydrolase against the peptidoglycan cell wall to allow the assembly of the T4SS apparatus. In the current study, the CHAP domain of VirB1-89K from S. suis 89K PAI was cloned and over-expressed in Escherichia coli, and its peptidoglycan-degrading activity in vitro was determined. The results indicated that the VirB1-89K CHAP domain can degrade the peptidoglycan layer of bacteria. Deletion of virB1-89K reduces significantly, but does not abolish, the virulence of S. suis in a mouse model. CONCLUSIONS The experimental results presented here suggested that VirB1-89K facilitates the assembly of 89K T4SS apparatus by catalyzing the degradation of the peptidoglycan cell wall, thus contributing to the pathogenesis of S. suis 2 infection.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | - Fuquan Hu
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
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Inducible cell lysis systems in microbial production of bio-based chemicals. Appl Microbiol Biotechnol 2013; 97:7121-9. [DOI: 10.1007/s00253-013-5100-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2013] [Revised: 07/04/2013] [Accepted: 07/05/2013] [Indexed: 02/02/2023]
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8
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Dessau M, Goldhill D, McBride RL, Turner PE, Modis Y. Selective pressure causes an RNA virus to trade reproductive fitness for increased structural and thermal stability of a viral enzyme. PLoS Genet 2012; 8:e1003102. [PMID: 23209446 PMCID: PMC3510033 DOI: 10.1371/journal.pgen.1003102] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Accepted: 10/03/2012] [Indexed: 11/18/2022] Open
Abstract
The modulation of fitness by single mutational substitutions during environmental change is the most fundamental consequence of natural selection. The antagonistic tradeoffs of pleiotropic mutations that can be selected under changing environments therefore lie at the foundation of evolutionary biology. However, the molecular basis of fitness tradeoffs is rarely determined in terms of how these pleiotropic mutations affect protein structure. Here we use an interdisciplinary approach to study how antagonistic pleiotropy and protein function dictate a fitness tradeoff. We challenged populations of an RNA virus, bacteriophage Φ6, to evolve in a novel temperature environment where heat shock imposed extreme virus mortality. A single amino acid substitution in the viral lysin protein P5 (V207F) favored improved stability, and hence survival of challenged viruses, despite a concomitant tradeoff that decreased viral reproduction. This mutation increased the thermostability of P5. Crystal structures of wild-type, mutant, and ligand-bound P5 reveal the molecular basis of this thermostabilization--the Phe207 side chain fills a hydrophobic cavity that is unoccupied in the wild-type--and identify P5 as a lytic transglycosylase. The mutation did not reduce the enzymatic activity of P5, suggesting that the reproduction tradeoff stems from other factors such as inefficient capsid assembly or disassembly. Our study demonstrates how combining experimental evolution, biochemistry, and structural biology can identify the mechanisms that drive the antagonistic pleiotropic phenotypes of an individual point mutation in the classic evolutionary tug-of-war between survival and reproduction.
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Affiliation(s)
- Moshe Dessau
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut, United States of America
| | - Daniel Goldhill
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, United States of America
| | - Robert L. McBride
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, United States of America
| | - Paul E. Turner
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, United States of America
| | - Yorgo Modis
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut, United States of America
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9
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Characterization of peptidoglycan hydrolase in Cag pathogenicity island of Helicobacter pylori. Mol Biol Rep 2010; 38:503-9. [PMID: 20358296 DOI: 10.1007/s11033-010-0134-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2009] [Accepted: 03/23/2010] [Indexed: 10/19/2022]
Abstract
The Cag Type IV secretion apparatus proteins in Helicobacter pylori can mediate the injection of effector CagA protein into eukaryotic target cells. Although this apparatus forms an important pathway for bacterium-host interaction, its assembly process in vivo is poorly understood, and the proteins which contribute to break the bacterial cell walls in Cag-PAI have not yet been identified. The cagγ gene in Cag-PAI is a unique member that contains a conserved SLT catalysis domain, which makes it an attracting question whether cagy gene has the capacity to digest the bacterial cell wall. In the current study, therefore, the cagγ gene was cloned from the H. pylori NCTC 11637 and expressed in Escherichia coli, and its lytic effect on cell walls in vitro was observed. Results indicated that Cagγ protein has a lytic activity against bacterial cell walls. An allelic-exchange mutant (Δcagγ) was further constructed to investigate the relationship between Cagγ and effector CagA translocation. These results suggested that Cagγ contributed to the assembly of Cag Type IV secretion apparatus by digesting the peptidoglycan meshwork of bacterial cell walls.
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Abstract
We designed and constructed a controllable inducing lysis system in Synechocystis sp. PCC 6803 to facilitate extracting lipids for biofuel production. Several bacteriophage-derived lysis genes were integrated into the genome and placed downstream of a nickel-inducible signal transduction system. We applied 3 strategies: (i) directly using the phage lysis cassette, (ii) constitutively expressing endolysin genes while restricting holin genes, and (iii) combining lysis genes from different phages. Significant autolysis was induced in the Synechocystis sp. PCC 6803 cells with this system by the addition of NiSO(4). Our inducible cyanobacterial lysing system eliminates the need for mechanical or chemical cell breakage and could facilitate recovery of biofuel from cyanobacteria.
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11
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Scheurwater EM, Clarke AJ. The C-terminal domain of Escherichia coli YfhD functions as a lytic transglycosylase. J Biol Chem 2008; 283:8363-73. [PMID: 18234673 DOI: 10.1074/jbc.m710135200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The hypothetical Escherichia coli protein YfhD has been identified as the archetype for the family 1B lytic transglycosylases despite a complete lack of experimental characterization. The yfhD gene was amplified from the genomic DNA of E. coli W3110 and cloned to encode a fusion protein with a C-terminal His(6) sequence. The enzyme was found to be localized to the outer membrane of E. coli, as would be expected for a lytic transglycosylase. Its gene was engineered for the production of a truncated soluble enzyme derivative lacking an N-terminal signal sequence and membrane anchor. The soluble YfhD derivative was purified to apparent homogeneity, and three separate in vitro assays involving high pressure liquid chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry were used to demonstrate the YfhD-catalyzed release of 1,6-anhydromuro-peptides from insoluble peptidoglycan. In addition, an in vivo bioassay developed using the bacteriophage lambda lysis system confirmed that the enzyme functions as an autolysin. Based on these data, the enzyme was renamed membrane-bound lytic transglycosylase F. The modular structure of MltF was investigated through genetic engineering for the separate production of identified N-terminal and C-terminal domains. The ability to bind peptidoglycan and lytic activity were only associated with the isolated C-terminal domain. The enzymatic properties of this lytic transglycosylase domain were found to be very similar to those of the wild-type enzyme. The one notable exception was that the N-terminal domain appears to modulate the lytic behavior of the C-terminal domain to permit continued lysis of insoluble peptidoglycan, a unique feature of MltF compared with other characterized lytic transglycosylases.
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Affiliation(s)
- Edie M Scheurwater
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
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Reid CW, Legaree BA, Clarke AJ. Role of Ser216 in the mechanism of action of membrane-bound lytic transglycosylase B: Further evidence for substrate-assisted catalysis. FEBS Lett 2007; 581:4988-92. [PMID: 17910958 DOI: 10.1016/j.febslet.2007.09.037] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2007] [Accepted: 09/19/2007] [Indexed: 11/21/2022]
Abstract
Lytic transglycosylases cleave the beta-(1-->4)-glycosidic bond in the bacterial cell wall heteropolymer peptidoglycan between the N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) residues with the concomitant formation of a 1,6-anhydromuramoyl residue. Based on sequence alignments, Ser216 in Pseudomonas aeruginosa membrane-bound lytic transglycosylase B (MltB) was targeted for replacement with alanine to delineate its role in the enzyme's mechanism of action. The specific activity of the Ser216-->Ala MltB derivative was less than 12% of that for the wild-type enzyme, while its substrate binding affinity remained virtually unaltered. These data are in agreement with a role of Ser216 in orienting the N-acetyl group on MurNAc at the -1 subsite of MltB for its participation in a substrate-assisted mechanism of action.
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Affiliation(s)
- Christopher W Reid
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
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Pagliero E, Dideberg O, Vernet T, Di Guilmi AM. The PECACE domain: a new family of enzymes with potential peptidoglycan cleavage activity in Gram-positive bacteria. BMC Genomics 2005; 6:19. [PMID: 15717932 PMCID: PMC550655 DOI: 10.1186/1471-2164-6-19] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2004] [Accepted: 02/17/2005] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The metabolism of bacterial peptidoglycan is a dynamic process, synthases and cleavage enzymes are functionally coordinated. Lytic Transglycosylase enzymes (LT) are part of multienzyme complexes which regulate bacterial division and elongation. LTs are also involved in peptidoglycan turnover and in macromolecular transport systems. Despite their central importance, no LTs have been identified in the human pathogen Streptococcus pneumoniae. We report the identification of the first putative LT enzyme in S. pneumoniae and discuss its role in pneumococcal peptidoglycan metabolism. RESULTS Homology searches of the pneumococcal genome allowed the identification of a new domain putatively involved in peptidoglycan cleavage (PECACE, PEptidoglycan CArbohydrate Cleavage Enzyme). This sequence has been found exclusively in Gram-positive bacteria and gene clusters containing pecace are conserved among Streptococcal species. The PECACE domain is, in some instances, found in association with other domains known to catalyze peptidoglycan hydrolysis. CONCLUSIONS A new domain, PECACE, putatively involved in peptidoglycan hydrolysis has been identified in S. pneumoniae. The probable enzymatic activity deduced from the detailed analysis of the amino acid sequence suggests that the PECACE domain may proceed through a LT-type or goose lyzosyme-type cleavage mechanism. The PECACE function may differ largely from the other hydrolases already identified in the pneumococcus: LytA, LytB, LytC, CBPD and PcsB. The multimodular architecture of proteins containing the PECACE domain is another example of the many activities harbored by peptidoglycan hydrolases, which is probably required for the regulation of peptidoglycan metabolism. The release of new bacterial genomes sequences will probably add new members to the five groups identified so far in this work, and new groups could also emerge. Conversely, the functional characterization of the unknown domains mentioned in this work can now become easier, since bacterial peptidoglycan is proposed to be the substrate.
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Affiliation(s)
- Estelle Pagliero
- Laboratoire d'Ingénierie des Macromolécules Institute de Biologie Structurale Jean-Pierre Ebel (CEA-CNRS UMR 5075-UJF), 41 Rue Jules Horowitz 38027 Grenoble cedex 1, France
| | - Otto Dideberg
- Laboratoire de Cristallographie Macromoléculaire Institut de Biologie Structurale Jean-Pierre Ebel (CEA-CNRS UMR 5075-UJF), 41 Rue Jules Horowitz 38027 Grenoble cedex 1, France
| | - Thierry Vernet
- Laboratoire d'Ingénierie des Macromolécules Institute de Biologie Structurale Jean-Pierre Ebel (CEA-CNRS UMR 5075-UJF), 41 Rue Jules Horowitz 38027 Grenoble cedex 1, France
| | - Anne Marie Di Guilmi
- Laboratoire d'Ingénierie des Macromolécules Institute de Biologie Structurale Jean-Pierre Ebel (CEA-CNRS UMR 5075-UJF), 41 Rue Jules Horowitz 38027 Grenoble cedex 1, France
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14
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Reid CW, Blackburn NT, Legaree BA, Auzanneau FI, Clarke AJ. Inhibition of membrane-bound lytic transglycosylase B by NAG-thiazoline. FEBS Lett 2004; 574:73-9. [PMID: 15358542 DOI: 10.1016/j.febslet.2004.08.006] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2004] [Revised: 07/30/2004] [Accepted: 08/04/2004] [Indexed: 11/24/2022]
Abstract
The lytic transglycosylases cleave the bacterial cell wall heteropolymer peptidoglycan with the same specificity as the muramidases (lysozymes), between the N-acetylmuramic acid and N-acetylglucosamine residues, with the concomitant formation of a 1,6-anhydromuramoyl residue. The putative catalytic residue in the family 3 lytic transglycosylase from Pseudomonas aeruginosa, Glu162 as identified by sequence alignment to the homologous enzyme from Escherichia coli, was replaced with both Ala and Asp by site-directed mutagenesis. Neither mutant enzyme differed structurally from the wild-type enzyme, as judged by CD spectroscopy, but both were enzymatically inactive confirming the essential role of Glu162 in the mechanism of action of this lytic transglycosylase. The beta-hexosaminidase inhibitor NAG-thiazoline was shown to inhibit the activity of lytic transglycosylase activity, thus providing the first direct evidence that the formation of the 1,6-anhydromuramoyl residue may proceed through an oxazolinium ion intermediate involving anchimeric assistance. Using surface plasmon resonance and difference absorbance spectroscopy, Kd values of 1.8 and 1.4 mM, respectively, were determined for NAG thiazoline, while its parent compound N-acetylglucosamine neither inhibited nor appeared to bind the lytic transglycosylase with any significant affinity.
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Affiliation(s)
- C W Reid
- Guelph Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Guelph, Guelph, Ont., Canada N1G 2W1
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