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Hershko Y, Rannon E, Adler A, Burstein D, Barkan D. WarA, a remote homolog of NpmA and KamB from Nocardia wallacei, confers broad spectrum aminoglycoside resistance in Nocardia and Mycobacteria. Int J Antimicrob Agents 2024; 63:107089. [PMID: 38218322 DOI: 10.1016/j.ijantimicag.2024.107089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 12/24/2023] [Accepted: 01/07/2024] [Indexed: 01/15/2024]
Abstract
OBJECTIVES Aminoglycoside resistance in bacteria is typically conferred by specific drug-modifying enzymes. Infrequently, such resistance is achieved through 16S ribosomal RNA methyltransferases, such as NpmA and KamB encoded by Escherichia coli and Streptoalloteichus tenebrarius, respectively. These enzymes are not widespread and have not been described in Nocardia species to date. METHODS We report the genomic mining of 18 Nocardia wallacei isolates that were found to be specifically and substantially resistant to amikacin. RESULTS We identified a gene coding for a protein with very distant homology to NpmA and KamB. However, 3-D modeling revealed that the tertiary structure of these three proteins was highly similar. Cloning and expressing this gene in two susceptible bacteria Nocardia asteroides, and Mycobacterium smegmatis (another Actinobacterium) led to high-level, pan-aminoglycoside resistance in both cases. We named this gene warA (Wallacei Amikacin Resistance A). CONCLUSIONS This is the first description and experimental characterization of a gene of this family in Nocardia, and the first demonstration that such activity could lead to pan-aminoglycoside resistance in Mycobacteria as well. The discovery of this novel gene has important biotechnology and clinical implications.
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Affiliation(s)
- Yizhak Hershko
- Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel; Clinical Microbiology Laboratory, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel
| | - Ella Rannon
- The Shmunis School of Biomedicine and Cancer Research, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv, Israel
| | - Amos Adler
- Clinical Microbiology Laboratory, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel; Department of Epidemiology and Preventive Medicine, School of Public Health, Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - David Burstein
- The Shmunis School of Biomedicine and Cancer Research, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv, Israel
| | - Daniel Barkan
- Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
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2
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Hao M, Schuyler J, Zhang H, Shashkina E, Du H, Fouts DE, Satlin M, Kreiswirth BN, Chen L. Apramycin resistance in epidemic carbapenem-resistant Klebsiella pneumoniae ST258 strains. J Antimicrob Chemother 2021; 76:2017-2023. [PMID: 33942093 DOI: 10.1093/jac/dkab131] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Accepted: 03/31/2021] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Recent studies indicated that the monosubstituted deoxystreptamine aminoglycoside apramycin is a potent antibiotic against a wide range of MDR Gram-negative pathogens. OBJECTIVES To evaluate the in vitro activity of apramycin against carbapenem-resistant Klebsiella pneumoniae (CRKp) isolates from New York and New Jersey, and to explore mechanisms of apramycin resistance. METHODS Apramycin MICs were determined by broth microdilution for 155 CRKp bloodstream isolates collected from 2013 to 2018. MLST STs, wzi capsular types and apramycin resistance gene aac(3')-IV were examined by PCR and Sanger sequencing. Selected isolates were further characterized by conjugation experiments and WGS. RESULTS Apramycin MIC50/90 values were 8 and >128 mg/L for CRKp isolates, which are much higher than previously reported. Twenty-four isolates (15.5%) were apramycin resistant (MIC ≥64 mg/L) and they were all from the K. pneumoniae ST258 background. The 24 apramycin-resistant K. pneumoniae ST258 strains belonged to six different capsular types and 91.7% of them harboured the apramycin resistance gene aac(3')-IV. Sequencing analysis showed that different ST258 capsular type strains shared a common non-conjugative IncR plasmid, co-harbouring aac(3')-IV and blaKPC. A novel IncR and IncX3 cointegrate plasmid, p59494-RX116.1, was also identified in an ST258 strain, demonstrating how apramycin resistance can be spread from a non-conjugative plasmid through cointegration. CONCLUSIONS We described a high apramycin resistance rate in clinical CRKp isolates in the New York/New Jersey region, mainly among the epidemic K. pneumoniae ST258 strains. The high resistance rate in an epidemic K. pneumoniae clone raises concern regarding the further optimization and development of apramycin and apramycin-like antibiotics.
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Affiliation(s)
- Mingju Hao
- Department of Clinical Laboratory Medicine, The First Affiliated Hospital of Shandong First Medical University & Shandong Provincial Qianfoshan Hospital, Shandong Medicine and Health Key Laboratory of Laboratory Medicine, Jinan, Shandong, China
| | - Jessica Schuyler
- School of Graduate Studies, Rutgers University, Newark, NJ, USA.,Center for Discovery and Innovation, Hackensack-Meridian Health, Nutley, NJ, USA
| | - Haifang Zhang
- Department of Clinical Laboratory, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China
| | - Elena Shashkina
- Center for Discovery and Innovation, Hackensack-Meridian Health, Nutley, NJ, USA
| | - Hong Du
- Department of Clinical Laboratory, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China
| | | | - Michael Satlin
- Division of Infectious Diseases, Department of Medicine, Weill Cornell Medicine, New York, NY, USA
| | - Barry N Kreiswirth
- Center for Discovery and Innovation, Hackensack-Meridian Health, Nutley, NJ, USA
| | - Liang Chen
- Center for Discovery and Innovation, Hackensack-Meridian Health, Nutley, NJ, USA.,Department of Medical Sciences, Hackensack Meridian School of Medicine, Nutley, NJ, USA
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3
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Nosrati M, Dey D, Mehrani A, Strassler SE, Zelinskaya N, Hoffer ED, Stagg SM, Dunham CM, Conn GL. Functionally critical residues in the aminoglycoside resistance-associated methyltransferase RmtC play distinct roles in 30S substrate recognition. J Biol Chem 2019; 294:17642-17653. [PMID: 31594862 DOI: 10.1074/jbc.ra119.011181] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Revised: 10/03/2019] [Indexed: 11/06/2022] Open
Abstract
Methylation of the small ribosome subunit rRNA in the ribosomal decoding center results in exceptionally high-level aminoglycoside resistance in bacteria. Enzymes that methylate 16S rRNA on N7 of nucleotide G1405 (m7G1405) have been identified in both aminoglycoside-producing and clinically drug-resistant pathogenic bacteria. Using a fluorescence polarization 30S-binding assay and a new crystal structure of the methyltransferase RmtC at 3.14 Å resolution, here we report a structure-guided functional study of 30S substrate recognition by the aminoglycoside resistance-associated 16S rRNA (m7G1405) methyltransferases. We found that the binding site for these enzymes in the 30S subunit directly overlaps with that of a second family of aminoglycoside resistance-associated 16S rRNA (m1A1408) methyltransferases, suggesting that both groups of enzymes may exploit the same conserved rRNA tertiary surface for docking to the 30S. Within RmtC, we defined an N-terminal domain surface, comprising basic residues from both the N1 and N2 subdomains, that directly contributes to 30S-binding affinity. In contrast, additional residues lining a contiguous adjacent surface on the C-terminal domain were critical for 16S rRNA modification but did not directly contribute to the binding affinity. The results from our experiments define the critical features of m7G1405 methyltransferase-substrate recognition and distinguish at least two distinct, functionally critical contributions of the tested enzyme residues: 30S-binding affinity and stabilizing a binding-induced 16S rRNA conformation necessary for G1405 modification. Our study sets the scene for future high-resolution structural studies of the 30S-methyltransferase complex and for potential exploitation of unique aspects of substrate recognition in future therapeutic strategies.
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Affiliation(s)
- Meisam Nosrati
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Debayan Dey
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Atousa Mehrani
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306
| | - Sarah E Strassler
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Natalia Zelinskaya
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Eric D Hoffer
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Scott M Stagg
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306
| | - Christine M Dunham
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Graeme L Conn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
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4
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Substrate Recognition and Modification by a Pathogen-Associated Aminoglycoside Resistance 16S rRNA Methyltransferase. Antimicrob Agents Chemother 2017; 61:AAC.00077-17. [PMID: 28289026 DOI: 10.1128/aac.00077-17] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 03/03/2017] [Indexed: 01/07/2023] Open
Abstract
The pathogen-associated 16S rRNA methyltransferase NpmA catalyzes m1A1408 modification to block the action of structurally diverse aminoglycoside antibiotics. Here, we describe the development of a fluorescence polarization binding assay and its use, together with complementary functional assays, to dissect the mechanism of NpmA substrate recognition. These studies reveal that electrostatic interactions made by the NpmA β2/3 linker collectively are critical for docking of NpmA on a conserved 16S rRNA tertiary surface. In contrast, other NpmA regions (β5/β6 and β6/β7 linkers) contain several residues critical for optimal positioning of A1408 but are largely dispensable for 30S binding. Our data support a model for NpmA action in which 30S binding and adoption of a catalytically competent state are distinct: docking on 16S rRNA via the β2/3 linker necessarily precedes functionally critical 30S substrate-driven conformational changes elsewhere in NpmA. This model is also consistent with catalysis being completely positional in nature, as the most significant effects on activity arise from changes that impact binding or stabilization of the flipped A1408 conformation. Our results provide a molecular framework for aminoglycoside resistance methyltransferase action that may serve as a functional paradigm for related enzymes and a starting point for development of inhibitors of these resistance determinants.
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5
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Witek MA, Kuiper EG, Minten E, Crispell EK, Conn GL. A Novel Motif for S-Adenosyl-l-methionine Binding by the Ribosomal RNA Methyltransferase TlyA from Mycobacterium tuberculosis. J Biol Chem 2016; 292:1977-1987. [PMID: 28031456 DOI: 10.1074/jbc.m116.752659] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Revised: 12/27/2016] [Indexed: 12/23/2022] Open
Abstract
Capreomycin is a potent ribosome-targeting antibiotic that is an essential component of current antituberculosis treatments, particularly in the case of multidrug-resistant Mycobacterium tuberculosis (Mtb). Optimal capreomycin binding and Mtb ribosome inhibition requires ribosomal RNA methylation in both ribosome subunits by TlyA (Rv1694), an enzyme with dual 2'-O-methytransferase and putative hemolytic activities. Despite the important role of TlyA in capreomycin sensitivity and identification of inactivating mutations in the corresponding Mtb gene tlyA, which cause resistance to capreomycin, our current structural and mechanistic understanding of TlyA action remains limited. Here, we present structural and functional analyses of Mtb TlyA interaction with its obligatory co-substrate for methyltransferase activity, S-adenosyl-l-methionine (SAM). Despite adopting a complete class I methyltransferase fold containing conserved SAM-binding and catalytic motifs, the isolated TlyA carboxyl-terminal domain exhibits no detectable affinity for SAM. Further analyses identify a tetrapeptide motif (RXWV) in the TlyA interdomain linker as indispensable for co-substrate binding. Our results also suggest that structural plasticity of the RXWV motif could contribute to TlyA domain interactions, as well as specific recognition of its two structurally distinct ribosomal RNA targets. Our findings thus reveal a novel motif requirement for SAM binding by TlyA and set the stage for future mechanistic studies of TlyA substrate recognition and modification that underpin Mtb sensitivity to capreomycin.
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Affiliation(s)
- Marta A Witek
- From the Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Emily G Kuiper
- From the Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322; Department of Biochemistry, Cell and Developmental Biology Program, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Elizabeth Minten
- Department of Biochemistry, Cell and Developmental Biology Program, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Emily K Crispell
- the Microbiology and Molecular Genetics Program, Graduate Division of Biological and Biomedical Sciences, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Graeme L Conn
- From the Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322.
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6
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Patel S. Drivers of bacterial genomes plasticity and roles they play in pathogen virulence, persistence and drug resistance. INFECTION GENETICS AND EVOLUTION 2016; 45:151-164. [DOI: 10.1016/j.meegid.2016.08.030] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Revised: 08/26/2016] [Accepted: 08/27/2016] [Indexed: 12/11/2022]
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7
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Owings JP, Kuiper EG, Prezioso SM, Meisner J, Varga JJ, Zelinskaya N, Dammer EB, Duong DM, Seyfried NT, Albertí S, Conn GL, Goldberg JB. Pseudomonas aeruginosa EftM Is a Thermoregulated Methyltransferase. J Biol Chem 2015; 291:3280-90. [PMID: 26677219 DOI: 10.1074/jbc.m115.706853] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Indexed: 11/06/2022] Open
Abstract
Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that trimethylates elongation factor-thermo-unstable (EF-Tu) on lysine 5. Lysine 5 methylation occurs in a temperature-dependent manner and is generally only seen when P. aeruginosa is grown at temperatures close to ambient (25 °C) but not at higher temperatures (37 °C). We have previously identified the gene, eftM (for EF-Tu-modifying enzyme), responsible for this modification and shown its activity to be associated with increased bacterial adhesion to and invasion of respiratory epithelial cells. Bioinformatic analyses predicted EftM to be a Class I S-adenosyl-l-methionine (SAM)-dependent methyltransferase. An in vitro methyltransferase assay was employed to show that, in the presence of SAM, EftM directly trimethylates EF-Tu. A natural variant of EftM, with a glycine to arginine substitution at position 50 in the predicted SAM-binding domain, lacks both SAM binding and enzyme activity. Mass spectrometry analysis of the in vitro methyltransferase reaction products revealed that EftM exclusively methylates at lysine 5 of EF-Tu in a distributive manner. Consistent with the in vivo temperature dependence of methylation of EF-Tu, preincubation of EftM at 37 °C abolished methyltransferase activity, whereas this activity was retained when EftM was preincubated at 25 °C. Irreversible protein unfolding at 37 °C was observed, and we propose that this instability is the molecular basis for the temperature dependence of EftM activity. Collectively, our results show that EftM is a thermolabile, SAM-dependent methyltransferase that directly trimethylates lysine 5 of EF-Tu in P. aeruginosa.
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Affiliation(s)
- Joshua P Owings
- From the Department of Pediatrics, Division of Pulmonology, Allergy/Immunology, Cystic Fibrosis and Sleep and the Emory-Children's Center for Cystic Fibrosis Research, Emory University and Children's Healthcare of Atlanta, Atlanta, Georgia 30322, the Department of Microbiology, Immunology, and Cancer Biology, University of Virginia, Charlottesville, Virginia 22908
| | - Emily G Kuiper
- the Department of Biochemistry and the Biochemistry, Cell, and Developmental Biology Program and
| | - Samantha M Prezioso
- From the Department of Pediatrics, Division of Pulmonology, Allergy/Immunology, Cystic Fibrosis and Sleep and the Emory-Children's Center for Cystic Fibrosis Research, Emory University and Children's Healthcare of Atlanta, Atlanta, Georgia 30322, Microbiology and Molecular Genetics Program, Graduate Division of Biological and Biomedical Sciences, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Jeffrey Meisner
- From the Department of Pediatrics, Division of Pulmonology, Allergy/Immunology, Cystic Fibrosis and Sleep and the Emory-Children's Center for Cystic Fibrosis Research, Emory University and Children's Healthcare of Atlanta, Atlanta, Georgia 30322
| | - John J Varga
- From the Department of Pediatrics, Division of Pulmonology, Allergy/Immunology, Cystic Fibrosis and Sleep and the Emory-Children's Center for Cystic Fibrosis Research, Emory University and Children's Healthcare of Atlanta, Atlanta, Georgia 30322, the Department of Microbiology, Immunology, and Cancer Biology, University of Virginia, Charlottesville, Virginia 22908
| | | | | | | | | | - Sebastián Albertí
- the Instituto Universitario de Investigación en Ciencias de la Salud, Universidad de las Islas Baleares, Palma de Mallorca, 07122 Spain
| | | | - Joanna B Goldberg
- From the Department of Pediatrics, Division of Pulmonology, Allergy/Immunology, Cystic Fibrosis and Sleep and the Emory-Children's Center for Cystic Fibrosis Research, Emory University and Children's Healthcare of Atlanta, Atlanta, Georgia 30322, the Department of Microbiology, Immunology, and Cancer Biology, University of Virginia, Charlottesville, Virginia 22908,
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8
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Witek MA, Conn GL. Functional dichotomy in the 16S rRNA (m1A1408) methyltransferase family and control of catalytic activity via a novel tryptophan mediated loop reorganization. Nucleic Acids Res 2015; 44:342-53. [PMID: 26609134 PMCID: PMC4705659 DOI: 10.1093/nar/gkv1306] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 11/09/2015] [Indexed: 12/29/2022] Open
Abstract
Methylation of the bacterial small ribosomal subunit (16S) rRNA on the N1 position of A1408 confers exceptionally high-level resistance to a broad spectrum of aminoglycoside antibiotics. Here, we present a detailed structural and functional analysis of the Catenulisporales acidiphilia 16S rRNA (m1A1408) methyltransferase (‘CacKam’). The apo CacKam structure closely resembles other m1A1408 methyltransferases within its conserved SAM-binding fold but the region linking core β strands 6 and 7 (the ‘β6/7 linker’) has a unique, extended structure that partially occludes the putative 16S rRNA binding surface, and sequesters the conserved and functionally critical W203 outside of the CacKam active site. Substitution of conserved residues in the SAM binding pocket reveals a functional dichotomy in the 16S rRNA (m1A1408) methyltransferase family, with two apparently distinct molecular mechanisms coupling cosubstrate/ substrate binding to catalytic activity. Our results additionally suggest that CacKam exploits the W203-mediated remodeling of the β6/7 linker as a novel mechanism to control 30S substrate recognition and enzymatic turnover.
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Affiliation(s)
- Marta A Witek
- Department of Biochemistry, Emory University School of Medicine, Atlanta GA 30322, USA
| | - Graeme L Conn
- Department of Biochemistry, Emory University School of Medicine, Atlanta GA 30322, USA
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9
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Heterologous Expression and Functional Characterization of the Exogenously Acquired Aminoglycoside Resistance Methyltransferases RmtD, RmtD2, and RmtG. Antimicrob Agents Chemother 2015; 60:699-702. [PMID: 26552988 DOI: 10.1128/aac.02482-15] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 11/06/2015] [Indexed: 11/20/2022] Open
Abstract
The exogenously acquired 16S rRNA methyltransferases RmtD, RmtD2, and RmtG were cloned and heterologously expressed in Escherichia coli, and the recombinant proteins were purified to near homogeneity. Each methyltransferase conferred an aminoglycoside resistance profile consistent with m(7)G1405 modification, and this activity was confirmed by in vitro 30S methylation assays. Analyses of protein structure and interaction with S-adenosyl-l-methionine suggest that the molecular mechanisms of substrate recognition and catalysis are conserved across the 16S rRNA (m(7)G1405) methyltransferase family.
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10
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The Pathogen-Derived Aminoglycoside Resistance 16S rRNA Methyltransferase NpmA Possesses Dual m1A1408/m1G1408 Specificity. Antimicrob Agents Chemother 2015; 59:7862-5. [PMID: 26416864 DOI: 10.1128/aac.01872-15] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Accepted: 09/20/2015] [Indexed: 01/08/2023] Open
Abstract
Chemical modification of 16S rRNA can confer exceptionally high-level resistance to a diverse set of aminoglycoside antibiotics. Here, we show that the pathogen-derived enzyme NpmA possesses dual m(1)A1408/m(1)G1408 activity, an unexpected property apparently unique among the known aminoglycoside resistance 16S rRNA (m(1)A1408) methyltransferases. Although the biological significance of this activity remains to be determined, such mechanistic variation in enzymes acquired by pathogens has significant implications for development of inhibitors of these emerging resistance determinants.
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Garneau-Tsodikova S, Labby KJ. Mechanisms of Resistance to Aminoglycoside Antibiotics: Overview and Perspectives. MEDCHEMCOMM 2015; 7:11-27. [PMID: 26877861 DOI: 10.1039/c5md00344j] [Citation(s) in RCA: 303] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Aminoglycoside (AG) antibiotics are used to treat many Gram-negative and some Gram-positive infections and, importantly, multidrug-resistant tuberculosis. Among various bacterial species, resistance to AGs arises through a variety of intrinsic and acquired mechanisms. The bacterial cell wall serves as a natural barrier for small molecules such as AGs and may be further fortified via acquired mutations. Efflux pumps work to expel AGs from bacterial cells, and modifications here too may cause further resistance to AGs. Mutations in the ribosomal target of AGs, while rare, also contribute to resistance. Of growing clinical prominence is resistance caused by ribosome methyltransferases. By far the most widespread mechanism of resistance to AGs is the inactivation of these antibiotics by AG-modifying enzymes. We provide here an overview of these mechanisms by which bacteria become resistant to AGs and discuss their prevalence and potential for clinical relevance.
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Affiliation(s)
- Sylvie Garneau-Tsodikova
- University of Kentucky, Department of Pharmaceutical Sciences, 789 South Limestone Street, Lexington, KY, USA. ; Tel: 859-218-1686
| | - Kristin J Labby
- Beloit College, Department of Chemistry, 700 College Street, Beloit, WI, USA. ; Tel: 608-363-2273
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30S Subunit-dependent activation of the Sorangium cellulosum So ce56 aminoglycoside resistance-conferring 16S rRNA methyltransferase Kmr. Antimicrob Agents Chemother 2015; 59:2807-16. [PMID: 25733511 DOI: 10.1128/aac.00056-15] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Accepted: 02/25/2015] [Indexed: 01/25/2023] Open
Abstract
Methylation of bacterial 16S rRNA within the ribosomal decoding center confers exceptionally high resistance to aminoglycoside antibiotics. This resistance mechanism is exploited by aminoglycoside producers for self-protection while functionally equivalent methyltransferases have been acquired by human and animal pathogenic bacteria. Here, we report structural and functional analyses of the Sorangium cellulosum So ce56 aminoglycoside resistance-conferring methyltransferase Kmr. Our results demonstrate that Kmr is a 16S rRNA methyltransferase acting at residue A1408 to confer a canonical aminoglycoside resistance spectrum in Escherichia coli. Kmr possesses a class I methyltransferase core fold but with dramatic differences in the regions which augment this structure to confer substrate specificity in functionally related enzymes. Most strikingly, the region linking core β-strands 6 and 7, which forms part of the S-adenosyl-l-methionine (SAM) binding pocket and contributes to base flipping by the m(1)A1408 methyltransferase NpmA, is disordered in Kmr, correlating with an exceptionally weak affinity for SAM. Kmr is unexpectedly insensitive to substitutions of residues critical for activity of other 16S rRNA (A1408) methyltransferases and also to the effects of by-product inhibition by S-adenosylhomocysteine (SAH). Collectively, our results indicate that adoption of a catalytically competent Kmr conformation and binding of the obligatory cosubstrate SAM must be induced by interaction with the 30S subunit substrate.
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