title: A SAM-dependent methyltransferase cotranscribed with arsenate reductase alters resistance to peptidyl transferase center-binding antibiotics in Azospirillum brasilense Sp7.
abstract: The genome of Azospirillum brasilense harbors a gene encoding S-adenosylmethionine-dependent methyltransferase, which is located downstream of an arsenate reductase gene. Both genes are cotranscribed and translationally coupled. When they were cloned and expressed individually in an arsenate-sensitive strain of Escherichia coli, arsenate reductase conferred tolerance to arsenate; however, methyltransferase failed to do so. Sequence analysis revealed that methyltransferase was more closely related to a PrmB-type N5-glutamine methyltransferase than to the arsenate detoxifying methyltransferase ArsM. Insertional inactivation of prmB gene in A. brasilense resulted in an increased sensitivity to chloramphenicol and resistance to tiamulin and clindamycin, which are known to bind at the peptidyl transferase center (PTC) in the ribosome. These observations suggested that the inability of prmB:km mutant to methylate L3 protein might alter hydrophobicity in the antibiotic-binding pocket of the PTC, which might affect the binding of chloramphenicol, clindamycin, and tiamulin differentially. This is the first report showing the role of PrmB-type N5-glutamine methyltransferases in conferring resistance to tiamulin and clindamycin in any bacterium.
authors.affiliation: Laboratory of Bacterial Genetics, School of Biotechnology, Faculty of Science, Banaras Hindu University, Varanasi, 221005, India.
authors.forename: Sudhir
authors.initials: S
authors.lastname: Singh
authors.forename: Chhaya
authors.initials: C
authors.lastname: Singh
authors.forename: Anil Kumar
authors.initials: AK
authors.lastname: Tripathi
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D053502:Arsenate Reductases / Q000235:genetics / Q000378:metabolism*; D015806:Azospirillum brasilense / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D002701:Chloramphenicol / Q000378:metabolism / Q000494:pharmacology; D002981:Clindamycin / Q000378:metabolism / Q000494:pharmacology; D003001:Cloning, Molecular; D004224:Diterpenes / Q000378:metabolism / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D055786:Gene Knockout Techniques; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D012270:Ribosomes / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D004224:Diterpenes; D002981:Clindamycin; D002701:Chloramphenicol; C014224:tiamulin; D053502:Arsenate Reductases; D008780:Methyltransferases