RESUMO
Introduction: Aminoglycosides like streptomycin are well-known for binding at specific regions of ribosome RNA and then acting as translation inhibitors. Nowadays, several pathogens have been detected to acquire an undefined strategy involving mutation at non structural ribosome genes like those acting as RNA methylases. rsmG is one of those genes which encodes an AdoMet-dependent methyltransferase responsible for the synthesis of m 7 G527 in the 530 loop of bacterial 16S rRNA. This loop is universally conserved, plays a key role in ribosomal accuracy, and is a target for streptomycin binding. Loss of the m 7 G527 modification confers low-level streptomycin resistance and may affect ribosomal functioning. Objectives: After taking into account genetic information indicating that some clinical isolates of human pathogens show streptomycin resistance associated with mutations at rsmG , we decided to explore new hot spots for mutation capable of impairing the RsmG in vivo function and of promoting low-level streptomycin resistance. Materials and methods: To gain insights into the molecular and genetic mechanism of acquiring this aminoglycoside resistance phenotype and the emergence of high-level streptomycin resistance in rsmG mutants, we mutated Escherichia coli rsmG and also performed a genotyping study on rpsL from several isolates showing the ability to grow at higher streptomycin concentrations than parental strains. Results: We found that the mutations at rpsL were preferentially present in these mutants, and we observed a clear synergy between rsmG and rpsL genes to induce streptomycin resistance. Conclusion: We contribute to understand a common mechanism that is probably transferable to other ribosome RNA methylase genes responsible for modifications at central sites for ribosome function.
Introducción. Los aminoglucósidos son moléculas antibióticas capaces de inhibir la síntesis de proteínas bacterianas tras su unión al ribosoma procariota. La resistencia a aminoglucósidos está clásicamente asociada a mutaciones en genes estructurales del ribosoma bacteriano; sin embargo, varios estudios recientes han demostrado, de forma recurrente, la presencia de un nuevo mecanismo dependiente de mutación que no involucra genes estructurales. El gen rsmG es uno de ellos y se caracteriza por codificar una metiltransferasa que sintetiza el nucleósido m 7 G527 localizado en el loop 530 del ribosoma bacteriano, este último caracterizado como sitio preferencial al cual se une la estreptomicina. Objetivo. Partiendo de las recientes asociaciones clínicas entre las mutaciones en el gen rsmG y la resistencia a estreptomicina, este estudio se propuso la caracterización de nuevos puntos calientes de mutación en este gen que puedan causar resistencia a estreptomicina usando Escherichia coli como modelo de estudio. Materiales y métodos. Se indagó sobre el mecanismo genético y molecular por el cual se adquiere la resistencia a estreptomicina y su transición a la resistencia a altas dosis mediante mutagénesis dirigida del gen rsmG y genotipificación del gen rpsL . Resultados. Se encontró que la mutación N39A en rsmG inactiva la proteína y se reportó un nuevo conjunto de mutaciones en rpsL que confieren resistencia a altas dosis de estreptomicina. Conclusiones. Aunque los mecanismos genéticos subyacentes permanecen sin esclarecer, se concluyó que dichos patrones secuenciales de mutación podrían tener lugar en otros genes modificadores del ARN bacteriano debido a la conservación evolutiva y al papel crítico que juegan tales modificaciones en la síntesis de proteínas.
Assuntos
Aminoglicosídeos/farmacologia , Antibacterianos/farmacologia , Farmacorresistência Bacteriana/genética , Proteínas de Escherichia coli/genética , Mutação de Sentido Incorreto , Metiltransferases/genética , Mutação Puntual , Processamento Pós-Transcricional do RNA/genética , RNA Bacteriano/metabolismo , /metabolismo , Estreptomicina/farmacologia , Sequência de Aminoácidos , Sítios de Ligação/genética , Domínio Catalítico/genética , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , Escherichia coli/efeitos dos fármacos , Escherichia coli/enzimologia , Metilação , Modelos Moleculares , Dados de Sequência Molecular , Metiltransferases/química , Metiltransferases/metabolismo , Filogenia , Conformação Proteica , RNA Bacteriano/genética , /genética , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Proteínas Ribossômicas/genética , Proteínas Ribossômicas/metabolismo , S-Adenosilmetionina/metabolismo , Alinhamento de Sequência , Análise de Sequência de DNA , Deleção de Sequência , Homologia de Sequência de AminoácidosRESUMO
BACKGROUND/AIMS: Azathioprine (AZA) has been widely used in the therapy of inflammatory bowel disease (IBD) and autoimmune hepatitis (AIH). However, studies evaluating the adverse effects of AZA in these two diseases are lacking. The aim of this study was to compare the adverse effects of AZA in Korean IBD and AIH patients. METHODS: Patients with IBD or AIH who were treated with AZA at Keimyung University Dongsan Medical Center (Daegu, Korea) between January 2002 and March 2011 were enrolled. Their medical records were reviewed retrospectively in terms of clinical characteristics and adverse effects of AZA. RESULTS: A total of 139 IBD patients and 55 AIH patients were finally enrolled. Thirty IBD patients (21.6%) and eight AIH patients (14.5%) experienced adverse effects of AZA. In particular, the prevalence of leukopenia was significantly higher in the IBD group than in the AIH group (p=0.026). T474C mutation was observed in three of 10 patients who were assessed for thiopurine methyltransferase (TPMT) genotype. CONCLUSIONS: IBD patients are at increased risk for the adverse effects of AZA compared with AIH patients, of which leukopenia was the most commonly observed. Therefore, IBD patients receiving AZA therapy should be carefully monitored.
Assuntos
Adolescente , Adulto , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Adulto Jovem , Azatioprina/efeitos adversos , Sequência de Bases , Genótipo , Hepatite Autoimune/tratamento farmacológico , Imunossupressores/efeitos adversos , Doenças Inflamatórias Intestinais/tratamento farmacológico , Leucopenia/epidemiologia , Metiltransferases/química , Polimorfismo de Nucleotídeo Único , República da Coreia , Estudos RetrospectivosRESUMO
Low temperature fluorescence spectra (FS) and fluorescence excitation spectra (FES) of protoporphyrin IX (Proto), Mg-protoporphyrin IX and its monomethyl ester (MgProto-ME) and protochlorophyllide (Pchlide) in etiolated barley leaves treated with 5-aminolevulinic acid and/or 2,2'-dipyridyl were studied. The spectra of Proto and MgProto-ME showed a little dependence on temperature of registration and exhibited similarity to low temperature spectra in diluted organic and buffer solutions. However, a red wavelength shift for Soret bands of Proto and MgProto-ME was observed due to porphyrin interaction with bovine serum albumin in 0.05 M, Na2HPO4 solution at room temperature. Disaggregating treatments had no effect on Proto and MgProto-ME spectra in plants. These results suggested that in etiolated leaves Proto and MgProto-ME molecules were in a monomer state. The spectral properties of these molecules were determined by interaction of porphyrins with proteins and other plastid membrane components. The spectral analyses indicated an efficient energy migration from Proto and MgProto-ME molecules to active form of Pchlide which emitted at 656nm, and no energy transfer from carotenoids to porphyrins in vivo. These findings suggested that Proto and MgProto-ME from carotenoids, and close location of these porphyrins and photoactive Pchlide in etioplast membranes. The latter conclusion was strongly supported by an observation that in etiolated leaves, S-adenosyl-L-methionin:Mg-protoporphyrin IX methyltransferase, which converts MgProto into MgProtoME, were located not only in prothylakoids but also in prolamellar bodies containing photoactive Pchlide.