Determination of the target nucleosides for members of two families of 16S rRNA methyltransferases that confer resistance to partially overlapping groups of aminoglycoside antibiotics.
The 16S ribosomal RNA methyltransferase enzymes that modify nucleosides in the drug binding site to provide self-resistance in aminoglycoside-producing micro-organisms have been proposed to comprise two distinct groups of S-adenosyl-l-methionine (SAM)-dependent RNA enzymes, namely the Kgm and Kam families. Here, the nucleoside methylation sites for three Kgm family methyltransferases, Sgm from Micromonospora zionensis, GrmA from Micromonospora echinospora and Krm from Frankia sp. Ccl3, were experimentally determined as G1405 by MALDI-ToF mass spectrometry. These results significantly extend the list of securely characterized G1405 modifying enzymes and experimentally validate their grouping into a single enzyme family. Heterologous expression of the KamB methyltransferase from Streptoalloteichus tenebrarius experimentally confirmed the requirement for an additional 60 amino acids on the deduced KamB N-terminus to produce an active methyltransferase acting at A1408, as previously suggested by an in silico analysis. Finally, the modifications at G1405 and A1408, were shown to confer partially overlapping but distinct resistance profiles in Escherichia coli. Collectively, these data provide a more secure and systematic basis for classification of new aminoglycoside resistance methyltransferases from producers and pathogenic bacteria on the basis of their sequences and resistance profiles.
Savic
Miloje
M
Faculty of Life Sciences, The University of Manchester, Manchester Interdisciplinary Biocentre, Manchester M1 7DN, UK.
Lovric
Josip
J
Tomic
Tatjana Ilic
TI
Vasiljevic
Branka
B
Conn
Graeme L
GL
D000617:Aminoglycosides / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects; D008780:Methyltransferases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D009705:Nucleosides / Q000378:metabolism; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000737:chemistry* / Q000378:metabolism*
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D009705:Nucleosides; D012336:RNA, Ribosomal, 16S; D008780:Methyltransferases; C078392:sgm protein, Micromonospora zionensis