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d'Udekem d'Acoz O, Hue F, Ye T, Wang L, Leroux M, Rajngewerc L, Tran T, Phan K, Ramirez MS, Reisner W, Tolmasky ME, Reyes-Lamothe R. Dynamics and quantitative contribution of the aminoglycoside 6'- N-acetyltransferase type Ib to amikacin resistance. mSphere 2024; 9:e0078923. [PMID: 38353533 DOI: 10.1128/msphere.00789-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Accepted: 01/09/2024] [Indexed: 02/27/2024] Open
Abstract
Aminoglycosides are essential components in the available armamentarium to treat bacterial infections. The surge and rapid dissemination of resistance genes strongly reduce their efficiency, compromising public health. Among the multitude of modifying enzymes that confer resistance to aminoglycosides, the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib] is the most prevalent and relevant in the clinical setting as it can inactivate numerous aminoglycosides, such as amikacin. Although the mechanism of action, structure, and biochemical properties of the AAC(6')-Ib protein have been extensively studied, the contribution of the intracellular milieu to its activity remains unclear. In this work, we used a fluorescent-based system to quantify the number of AAC(6')-Ib per cell in Escherichia coli, and we modulated this copy number with the CRISPR interference method. These tools were then used to correlate enzyme concentrations with amikacin resistance levels. Our results show that resistance to amikacin increases linearly with a higher concentration of AAC(6')-Ib until it reaches a plateau at a specific protein concentration. In vivo imaging of this protein shows that it diffuses freely within the cytoplasm of the cell, but it tends to form inclusion bodies at higher concentrations in rich culture media. Addition of a chelating agent completely dissolves these aggregates and partially prevents the plateau in the resistance level, suggesting that AAC(6')-Ib aggregation lowers resistance to amikacin. These results provide the first step in understanding the cellular impact of each AAC(6')-Ib molecule on aminoglycoside resistance. They also highlight the importance of studying its dynamic behavior within the cell.IMPORTANCEAntibiotic resistance is a growing threat to human health. Understanding antibiotic resistance mechanisms can serve as foundation for developing innovative treatment strategies to counter this threat. While numerous studies clarified the genetics and dissemination of resistance genes and explored biochemical and structural features of resistance enzymes, their molecular dynamics and individual contribution to resistance within the cellular context remain unknown. Here, we examined this relationship modulating expression levels of aminoglycoside 6'-N-acetyltransferase type Ib, an enzyme of clinical relevance. We show a linear correlation between copy number of the enzyme per cell and amikacin resistance levels up to a threshold where resistance plateaus. We propose that at concentrations below the threshold, the enzyme diffuses freely in the cytoplasm but aggregates at the cell poles at concentrations over the threshold. This research opens promising avenues for studying enzyme solubility's impact on resistance, creating opportunities for future approaches to counter resistance.
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Affiliation(s)
| | - Fong Hue
- Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, California, USA
- Department of Biological Science, California State University Fullerton, Fullerton, California, USA
| | - Tianyi Ye
- Department of Biology, McGill University, Montréal, Québec, Canada
| | - Louise Wang
- Department of Biology, McGill University, Montréal, Québec, Canada
| | - Maxime Leroux
- Department of Biology, McGill University, Montréal, Québec, Canada
| | - Lucila Rajngewerc
- Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, California, USA
- Department of Biological Science, California State University Fullerton, Fullerton, California, USA
| | - Tung Tran
- Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, California, USA
- Department of Biological Science, California State University Fullerton, Fullerton, California, USA
| | - Kimberly Phan
- Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, California, USA
- Department of Biological Science, California State University Fullerton, Fullerton, California, USA
| | - Maria S Ramirez
- Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, California, USA
- Department of Biological Science, California State University Fullerton, Fullerton, California, USA
| | - Walter Reisner
- Department of Physics, McGill University, Montréal, Québec, Canada
| | - Marcelo E Tolmasky
- Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, California, USA
- Department of Biological Science, California State University Fullerton, Fullerton, California, USA
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d'Acoz OD, Hue F, Ye T, Wang L, Leroux M, Rajngewerc L, Tran T, Phan K, Ramirez MS, Reisner W, Tolmasky ME, Reyes-Lamothe R. Dynamics and quantitative contribution of the aminoglycoside 6'- N-acetyltransferase type Ib [AAC(6')-Ib] to amikacin resistance. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.05.556435. [PMID: 38168340 PMCID: PMC10760054 DOI: 10.1101/2023.09.05.556435] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
Aminoglycosides are essential components in the available armamentarium to treat bacterial infections. The surge and rapid dissemination of resistance genes strongly reduce their efficiency, compromising public health. Among the multitude of modifying enzymes that confer resistance to aminoglycosides, the aminoglycoside acetyltransferase AAC(6')-Ib is the most prevalent and relevant in the clinical setting as it can inactivate numerous aminoglycosides, such as amikacin. Although the mechanism of action, structure, and biochemical properties of the AAC(6')-Ib protein have been extensively studied, the contribution of the intracellular milieu to its activity remains unclear. In this work, we used a fluorescent-based system to quantify the number of AAC(6')-Ib per cell in Escherichia coli, and we modulated this copy number with the CRISPR interference method. These tools were then used to correlate enzyme concentrations with amikacin resistance levels. Our results show that resistance to amikacin increases linearly with a higher concentration of AAC(6')-Ib until it reaches a plateau at a specific protein concentration. In vivo imaging of this protein shows that it diffuses freely within the cytoplasm of the cell, but it tends to form inclusion bodies at higher concentrations in rich culture media. Addition of a chelating agent completely dissolves these aggregates and partially prevents the plateau in the resistance level, suggesting that AAC(6')-Ib aggregation lowers resistance to amikacin. These results provide the first step in understanding the cellular impact of each AAC(6')-Ib molecule on aminoglycoside resistance. They also highlight the importance of studying its dynamic behavior within the cell.
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Affiliation(s)
- Ophélie d'Udekem d'Acoz
- Department of Biology, McGill University, 3649 Sir William Osler, Montréal, Québec, H3G 0B1, Canada
| | - Fong Hue
- Center for Applied Biotechnology Studies, Department of Biological Science, California State University Fullerton, Fullerton, California
| | - Tianyi Ye
- Department of Biology, McGill University, 3649 Sir William Osler, Montréal, Québec, H3G 0B1, Canada
| | - Louise Wang
- Department of Biology, McGill University, 3649 Sir William Osler, Montréal, Québec, H3G 0B1, Canada
| | - Maxime Leroux
- Department of Biology, McGill University, 3649 Sir William Osler, Montréal, Québec, H3G 0B1, Canada
| | - Lucila Rajngewerc
- Center for Applied Biotechnology Studies, Department of Biological Science, California State University Fullerton, Fullerton, California
| | - Tung Tran
- Center for Applied Biotechnology Studies, Department of Biological Science, California State University Fullerton, Fullerton, California
| | - Kimberly Phan
- Center for Applied Biotechnology Studies, Department of Biological Science, California State University Fullerton, Fullerton, California
| | - Maria S Ramirez
- Center for Applied Biotechnology Studies, Department of Biological Science, California State University Fullerton, Fullerton, California
| | - Walter Reisner
- Department of Physics, McGill University, 3600 rue université, Montréal, Québec, H3A 2T8, Canada
| | - Marcelo E Tolmasky
- Center for Applied Biotechnology Studies, Department of Biological Science, California State University Fullerton, Fullerton, California
| | - Rodrigo Reyes-Lamothe
- Department of Biology, McGill University, 3649 Sir William Osler, Montréal, Québec, H3G 0B1, Canada
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Insights into the Function of the N-Acetyltransferase SatA That Detoxifies Streptothricin in Bacillus subtilis and Bacillus anthracis. Appl Environ Microbiol 2019; 85:AEM.03029-18. [PMID: 30658980 DOI: 10.1128/aem.03029-18] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 01/09/2019] [Indexed: 11/20/2022] Open
Abstract
Acylation of epsilon amino groups of lysyl side chains is a widespread modification of proteins and small molecules in cells of all three domains of life. Recently, we showed that Bacillus subtilis and Bacillus anthracis encode the GCN5-related N-acetyltransferase (GNAT) SatA that can acetylate and inactivate streptothricin, which is a broad-spectrum antibiotic produced by actinomycetes in the soil. To determine functionally relevant residues of B. subtilis SatA (BsSatA), a mutational screen was performed, highlighting the importance of a conserved area near the C terminus. Upon inspection of the crystal structure of the B. anthracis Ames SatA (BaSatA; PDB entry 3PP9), this area appears to form a pocket with multiple conserved aromatic residues; we hypothesized this region contains the streptothricin-binding site. Chemical and site-directed mutagenesis was used to introduce missense mutations into satA, and the functionality of the variants was assessed using a heterologous host (Salmonella enterica). Results of isothermal titration calorimetry experiments showed that residue Y164 of BaSatA was important for binding streptothricin. Results of size exclusion chromatography analyses showed that residue D160 was important for dimerization. Together, these data advance our understanding of how SatA interacts with streptothricin.IMPORTANCE This work provides insights into how an abundant antibiotic found in soil is bound to the enzyme that inactivates it. This work identifies residues for the binding of the antibiotic and probes the contributions of substituting side chains for those in the native protein, providing information regarding hydrophobicity, size, and flexibility of the antibiotic binding site.
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Paiva MC, Reis MP, Costa PS, Dias MF, Bleicher L, Scholte LLS, Nardi RMD, Nascimento AMA. Identification of new bacteria harboring qnrS and aac(6')-Ib/cr and mutations possibly involved in fluoroquinolone resistance in raw sewage and activated sludge samples from a full-scale WWTP. WATER RESEARCH 2017; 110:27-37. [PMID: 27984803 DOI: 10.1016/j.watres.2016.11.056] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 11/22/2016] [Accepted: 11/23/2016] [Indexed: 06/06/2023]
Abstract
Wastewater treatment plants (WWTPs) harbor bacteria and antimicrobial resistance genes, favoring gene exchange events and resistance dissemination. Here, a culture-based and metagenomic survey of qnrA, qnrB, qnrS, and aac(6')-Ib genes from raw sewage (RS) and activated sludge (AS) of a full-scale municipal WWTP was performed. A total of 96 bacterial isolates were recovered from nalidixic acid-enrichment cultures. Bacteria harboring the aac(6')-Ib gene predominated in RS, whereas qnrS-positive isolates were specific to AS. Novel qnrS- and aac(6')-Ib-cr positive species were identified: Morganella morganii, Providencia rettgeri, and Pseudomonas guangdongensis (qnrS), and Alcaligenes faecalis and P. rettgeri (aac(6')-Ib-cr). Analysis of qnrS and aac(6')-Ib sequences from isolates and clone libraries suggested that the diversity of qnrS is wider than that of aac(6')-Ib. A large number of amino acid mutations were observed in the QnrS and AAC(6')-Ib proteins at previously undetected positions, whose structural implications are not clear. An accumulation of mutations at the C72, Q73, L74, A75 and M76 positions of QnrS, and D181 of AAC(6')-Ib might be important for resistance. These findings add significant information on bacteria harboring qnrS and aac(6')-Ib genes, and the presence of novel mutations that may eventually emerge in clinical isolates.
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Affiliation(s)
- Magna C Paiva
- Departamento de Microbiologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil; Campus Dona Lindu, Universidade Federal de São João del Rei, Divinópolis, Minas Gerais, Brazil
| | - Mariana P Reis
- Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
| | - Patrícia S Costa
- Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
| | - Marcela F Dias
- Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
| | - Lucas Bleicher
- Departamento de Bioquímica e Imunologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
| | - Larissa L S Scholte
- Centro de Pesquisas René Rachou - FIOCRUZ, Belo Horizonte, Minas Gerais, Brazil
| | - Regina M D Nardi
- Departamento de Microbiologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
| | - Andréa M A Nascimento
- Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
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5
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Ramirez MS, Nikolaidis N, Tolmasky ME. Rise and dissemination of aminoglycoside resistance: the aac(6')-Ib paradigm. Front Microbiol 2013; 4:121. [PMID: 23730301 PMCID: PMC3656343 DOI: 10.3389/fmicb.2013.00121] [Citation(s) in RCA: 114] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Accepted: 04/29/2013] [Indexed: 11/21/2022] Open
Abstract
Enzymatic modification is a prevalent mechanism by which bacteria defeat the action of antibiotics. Aminoglycosides are often inactivated by aminoglycoside modifying enzymes encoded by genes present in the chromosome, plasmids, and other genetic elements. The AAC(6′)-Ib (aminoglycoside 6′-N-acetyltransferase type Ib) is an enzyme of clinical importance found in a wide variety of gram-negative pathogens. The AAC(6′)-Ib enzyme is of interest not only because of his ubiquity but also because of other characteristics, it presents significant microheterogeneity at the N-termini and the aac(6′)-Ib gene is often present in integrons, transposons, plasmids, genomic islands, and other genetic structures. Excluding the highly heterogeneous N-termini, there are 45 non-identical AAC(6′)-Ib related entries in the NCBI database, 32 of which have identical name in spite of not having identical amino acid sequence. While some variants conserved similar properties, others show dramatic differences in specificity, including the case of AAC(6′)-Ib-cr that mediates acetylation of ciprofloxacin representing a rare case where a resistance enzyme acquires the ability to utilize an antibiotic of a different class as substrate. Efforts to utilize antisense technologies to turn off expression of the gene or to identify enzymatic inhibitors to induce phenotypic conversion to susceptibility are under way.
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Affiliation(s)
- María S Ramirez
- Department of Biological Science, Center for Applied Biotechnology Studies, College of Natural Sciences and Mathematics, California State University Fullerton Fullerton, CA, USA
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6
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Vong K, Auclair K. Understanding and overcoming aminoglycoside resistance caused by N-6'-acetyltransferase. MEDCHEMCOMM 2012; 3:397-407. [PMID: 28018574 PMCID: PMC5179255 DOI: 10.1039/c2md00253a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Aminoglycosides occupy a special niche amongst antibiotics in part because of their broad spectrum of action. Bacterial resistance is however menacing to render these drugs obsolete. A significant amount of work has been devoted to understand and overcome aminoglycoside resistance. This mini-review will discuss aminoglycoside-modifying enzymes (AMEs), with a special emphasis on the efforts to comprehend and block resistance caused by aminoglycoside 6'-N-acetyltransferase (AAC(6')).
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Affiliation(s)
- Kenward Vong
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montréal, Québec, Canada H3A 2K6
| | - Karine Auclair
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montréal, Québec, Canada H3A 2K6
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Abstract
Aminoglycosides have been an essential component of the armamentarium in the treatment of life-threatening infections. Unfortunately, their efficacy has been reduced by the surge and dissemination of resistance. In some cases the levels of resistance reached the point that rendered them virtually useless. Among many known mechanisms of resistance to aminoglycosides, enzymatic modification is the most prevalent in the clinical setting. Aminoglycoside modifying enzymes catalyze the modification at different -OH or -NH₂ groups of the 2-deoxystreptamine nucleus or the sugar moieties and can be nucleotidyltransferases, phosphotransferases, or acetyltransferases. The number of aminoglycoside modifying enzymes identified to date as well as the genetic environments where the coding genes are located is impressive and there is virtually no bacteria that is unable to support enzymatic resistance to aminoglycosides. Aside from the development of new aminoglycosides refractory to as many as possible modifying enzymes there are currently two main strategies being pursued to overcome the action of aminoglycoside modifying enzymes. Their successful development would extend the useful life of existing antibiotics that have proven effective in the treatment of infections. These strategies consist of the development of inhibitors of the enzymatic action or of the expression of the modifying enzymes.
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Pourreza A, Witherspoon M, Fox J, Newmark J, Bui D, Tolmasky ME. Mutagenesis analysis of a conserved region involved in acetyl coenzyme A binding in the aminoglycoside 6'-N-acetyltransferase type Ib encoded by plasmid pJHCMW1. Antimicrob Agents Chemother 2005; 49:2979-82. [PMID: 15980378 PMCID: PMC1168681 DOI: 10.1128/aac.49.7.2979-2982.2005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Alanine scanning of motif A in the pJHCMW1-encoded aminoglycoside 6'-N-acetyltransferase type Ib identified amino acids important for the ability of the enzyme to confer wild-type levels of resistance to kanamycin and amikacin. The replacement of two amino acids, D117 or L120, with alanine residues resulted in complete loss of the resistance phenotype.
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Affiliation(s)
- Atousa Pourreza
- Department of Biological Science, School of Natural Sciences and Mathematics, California State University Fullerton, Fullerton, California 92834-6850, USA
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Sarno R, Ha H, Weinsetel N, Tolmasky ME. Inhibition of aminoglycoside 6'-N-acetyltransferase type Ib-mediated amikacin resistance by antisense oligodeoxynucleotides. Antimicrob Agents Chemother 2004; 47:3296-304. [PMID: 14506044 PMCID: PMC201158 DOI: 10.1128/aac.47.10.3296-3304.2003] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Amikacin has been very useful in the treatment of infections caused by multiresistant bacteria because it is refractory to the actions of most modifying enzymes. However, the spread of AAC(6')-I-type acetyltransferases, enzymes capable of catalyzing inactivation of amikacin, has rendered this antibiotic all but useless in some parts of the world. The aminoglycoside 6'-N-acetyltransferase type Ib, which is coded for by the aac(6')-Ib gene, mediates resistance to amikacin and other aminoglycosides. RNase H mapping and computer prediction of the secondary structure led to the identification of five regions accessible for interaction with antisense oligodeoxynucleotides in the aac(6')-Ib mRNA. Oligodeoxynucleotides targeting these regions could bind to native mRNA with different efficiencies and mediated RNase H digestion. Selected oligodeoxynucleotides inhibited AAC(6')-Ib synthesis in cell-free coupled transcription-translation assays. After their introduction into an Escherichia coli strain harboring aac(6')-Ib by electroporation, some of these oligodeoxynucleotides decreased the level of resistance to amikacin. Our results indicate that use of antisense compounds could be a viable strategy to preserve the efficacies of existing antibiotics to which bacteria are becoming increasingly resistant.
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MESH Headings
- Acetyltransferases/antagonists & inhibitors
- Acetyltransferases/genetics
- Acetyltransferases/metabolism
- Amikacin/pharmacology
- Base Sequence
- Binding Sites
- Cell-Free System
- Colony Count, Microbial
- Drug Resistance, Multiple, Bacterial/drug effects
- Drug Resistance, Multiple, Bacterial/genetics
- Drug Resistance, Multiple, Bacterial/physiology
- Enzyme Inhibitors/pharmacology
- Escherichia coli/drug effects
- Escherichia coli/genetics
- Molecular Sequence Data
- Nucleic Acid Conformation
- Oligonucleotides, Antisense/genetics
- Oligonucleotides, Antisense/metabolism
- Oligonucleotides, Antisense/pharmacology
- Protein Biosynthesis
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Ribonuclease H/metabolism
- Transcription, Genetic
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Affiliation(s)
- Renee Sarno
- Department of Biological Science, College of Natural Science and Mathematics, California State University Fullerton, Fullerton, California 92834-6850, USA
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Dery KJ, Søballe B, Witherspoon MSL, Bui D, Koch R, Sherratt DJ, Tolmasky ME. The aminoglycoside 6'-N-acetyltransferase type Ib encoded by Tn1331 is evenly distributed within the cell's cytoplasm. Antimicrob Agents Chemother 2003; 47:2897-902. [PMID: 12936992 PMCID: PMC182613 DOI: 10.1128/aac.47.9.2897-2902.2003] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The multiresistance transposon Tn1331, which mediates resistance to several aminoglycosides and beta-lactams, includes the aac(6')-Ib, aadA1, bla(OXA-9), and bla(TEM-1) genes. The nucleotide sequence of aac(6')-Ib includes a region identical to that of the bla(TEM-1) gene. This region encompasses the promoter and the initiation codon followed by 15 nucleotides. Since there were three possible translation initiation sites, the amino acid sequence at the N terminus of the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib] was determined and was found to be SIQHF. This result indicated that aac(6')-Ib includes a translational fusion: the first five amino acids of the leader peptide of the TEM beta-lactamase are fused to the rest of the AAC(6')-Ib protein. This gene fusion could have formed during the genesis of Tn1331 as a consequence of the generation of a 520-nucleotide duplication (M. E. Tolmasky, Plasmid 24:218-226, 1990). An identical gene isolated from a Serratia marcescens strain has been previously described (G. Tran van Nhieu and E. Collatz, J. Bacteriol. 169:5708-5714, 1987). Extraction of the periplasmic proteins of E. coli harboring aac(6')-Ib by spheroplast formation showed that most of the AAC(6')-Ib protein is present in the cytoplasm. A genetic fusion to phoA confirmed these results. AAC(6')-Ib was shown to be evenly distributed inside the cell's cytoplasm by fluorescent microscopy with an AAC(6')-Ib-cyan fluorescent protein fusion.
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Affiliation(s)
- Ken J Dery
- Department of Biological Science, College of Natural Science and Mathematics, California State University Fullerton, Fullerton, California 92834-6850, USA
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11
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Shmara A, Weinsetel N, Dery KJ, Chavideh R, Tolmasky ME. Systematic analysis of a conserved region of the aminoglycoside 6'-N-acetyltransferase type Ib. Antimicrob Agents Chemother 2001; 45:3287-92. [PMID: 11709299 PMCID: PMC90828 DOI: 10.1128/aac.45.12.3287-3292.2001] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Alanine-scanning mutagenesis was applied to the aminoglycoside 6'-N-acetyltransferase type Ib conserved motif B, and the effects of the substitutions were analyzed by measuring the MICs of kanamycin (KAN) and its semisynthetic derivative, amikacin (AMK). Several substitutions resulted in no major change in MICs. E167A and F171A resulted in derivatives that lost the ability to confer resistance to KAN and AMK. P155A, P157A, N159A, L160A, I163A, K168A, and G170A conferred intermediate levels of resistance. Y166A resulted in an enzyme derivative with a modified specificity; it conferred a high level of resistance to KAN but lost the ability to confer resistance to AMK. Although not as pronounced, the resistance profiles conferred by substitutions N159A and G170A were related to that conferred by Y166A. These phenotypes, taken together with previous results indicating that mutant F171L could not catalyze acetylation of AMK when the assays were carried out at 42 degrees C (D. Panaite and M. Tolmasky, Plasmid 39:123-133, 1998), suggest that some motif B amino acids play a direct or indirect role in acceptor substrate specificity. MICs of AMK and KAN for cells harboring the substitution C165A were high, suggesting that the active form of the enzyme may not be a dimer formed through a disulfide bond. Furthermore, this result indicated that the acetylation reaction occurs through a direct mechanism rather than a ping-pong mechanism that includes a transient transfer of the acetyl group to a cysteine residue. Deletion of fragments at the C terminus demonstrated that up to 10 amino acids could be deleted without a loss of activity.
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Affiliation(s)
- A Shmara
- Institute of Molecular Biology and Nutrition, Department of Biological Science, College of Natural Sciences and Mathematics, California State University Fullerton, Fullerton, California 92834-6850, USA
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12
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Lu X, Hirata H, Yamaji Y, Ugaki M, Namba S. Random mutagenesis in a plant viral genome using a DNA repair-deficient mutator Escherichia coli strain. J Virol Methods 2001; 94:37-43. [PMID: 11337038 DOI: 10.1016/s0166-0934(01)00270-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Random mutagenesis in a plant viral genome is valuable for generating attenuated strains or for analyzing viral gene function at the molecular level. A DNA repair-deficient mutator Escherichia coli strain was used for random mutagenesis of a plant viral genome. A full-length infectious cDNA clone of Citrus tatter leaf virus (genus Capillovirus) L strain (CTLV-L) genomic RNA under the T7 promoter sequence (pITCL) was introduced into the mutator E. coli strain XL1-Red and mutagenized overnight. To fix mutations, the mixture of plasmid DNA isolated from colonies of the mutator bacteria was introduced into another E. coli strain, JM109, which has normal DNA repair function. Infectious viral genomic RNA was transcribed in vitro from each mutagenized pITCL clone and inoculated on host plants. Phenotypic mutants were selected for altered pathogenicity in the inoculated plants. Nucleotide sequence analysis of each mutant revealed that mutations were introduced randomly into the CTLV-L genome regardless of the function of the viral gene. The nucleotide substitutions were biased towards single point mutations, which consisted of more transitions than transversions or single-base frameshifts. These mutations were preserved stably in plants subject to sequential mechanical inoculation. The strategy presented below is a simple and very efficient way to generate virus mutants for analyzing the functions of viral genes.
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Affiliation(s)
- X Lu
- Laboratory of Bioresource Technology, Graduate School of Frontier Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, 113-8657, Tokyo, Japan
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13
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Chavideh R, Sholly S, Panaite D, Tolmasky ME. Effects of F171 mutations in the 6'-N-acetyltransferase type Ib [AAC(6')-Ib] enzyme on susceptibility to aminoglycosides. Antimicrob Agents Chemother 1999; 43:2811-2. [PMID: 10543772 PMCID: PMC89568 DOI: 10.1128/aac.43.11.2811] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Substitutions at position F171 of 6'-N-acetyltransferase type Ib cause variable loss of aminoglycoside resistance, indicating that this residue plays an important role in the structure and/or function of the enzyme.
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Affiliation(s)
- R Chavideh
- Institute of Molecular Biology, Department of Biological Science, School of Natural Sciences and Mathematics, California State University Fullerton, Fullerton, California 92834-6850, USA
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Barros JC, Pinheiro SR, Bozza M, Gueiros-Filho FJ, Bello AR, Lopes UG, Pereira JA. Evidences of gentamicin resistance amplification in Klebsiella pneumoniae isolated from faeces of hospitalized newborns. Mem Inst Oswaldo Cruz 1999; 94:795-802. [PMID: 10585658 DOI: 10.1590/s0074-02761999000600016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The intestinal microbiota, a barrier to the establishment of pathogenic bacteria, is also an important reservoir of opportunistic pathogens. It plays a key role in the process of resistance-genes dissemination, commonly carried by specialized genetic elements, like plasmids, phages, and conjugative transposons. We obtained from strains of enterobacteria, isolated from faeces of newborns in a university hospital nursery, indication of phenotypical gentamicin resistance amplification (frequencies of 10(-3) to 10(-5), compatible with transposition frequencies). Southern blotting assays showed strong hybridization signals for both plasmidial and chromosomal regions in DNA extracted from variants selected at high gentamicin concentrations, using as a probe a labeled cloned insert containing aminoglycoside modifying enzyme (AME) gene sequence originated from a plasmid of a Klebsiella pneumoniae strain previously isolated in the same hospital. Further, we found indications of inactivation to other resistance genes in variants selected under similar conditions, as well as, indications of co-amplification of other AME markers (amikacin). Since the intestinal environment is a scenario of selective processes due to the therapeutic and prophylactic use of antimicrobial agents, the processes of amplification of low level antimicrobial resistance (not usually detected or sought by common methods used for antibiotic resistance surveillance) might compromise the effectiveness of antibiotic chemotherapy.
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Affiliation(s)
- J C Barros
- Departamento de Patologia e Laboratórios, Faculdade de Ciências Médicas, UERJ, Rio de Janeiro, RJ, 20551-030, Brasil
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