engleski

Mutational analysis of basic residues in the N-terminal part of the rRNA : m6A methyltransferase ErmC'

Erm methyltransferases mediate the resistance to the macrolide-lincosamide-streptogramin B antibiotics via dimethylation of a specific adenine residue in 23 S rRNA. In spite of the biomedical importance of this process, virtually nothing is known about the function of N- and C-terminal sequence regions, which are unique to Erm methyltransferases. To define the role of positively charged N-terminal residues of the ErmC' methyltransferase in RNA binding and/or catalysis, we have undertaken the mutational analysis of amino acids K4 and K7 and characterized mutants in vivo and in vitro. Our results suggest that K4 and K7 residues are dispensable for the enzyme activity, however they seem to considerably support the catalytic step of the reaction, probably by maintaining the optimal conformation of the transition state through interactions with the phosphate backbone of RNA.

site-directed mutagenesis; antibiotic resistance; methylation; RNA binding; catalysis

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