"Structure and function of the antibiotic resistance-mediating methyltransferase AviRb from Streptomyces viridochromogenes."

Mosbacher TG, Bechthold A, Schulz GE



Published 2005-02-21 in J Mol Biol volume 345 .

Pubmed ID: 15581897
DOI identifier: -

Abstract:
The emergence of antibiotic-resistant bacterial strains is a widespread problem in medical practice and drug design, and each case requires the elucidation of the underlying mechanism. AviRb from Streptomyces viridochromogenes methylates the 2'-O atom of U2479 of the 23S ribosomal RNA in Gram-positive bacteria and thus mediates resistance to the oligosaccharide (orthosomycin) antibiotic avilamycin. The structure of AviRb with and without bound cofactor S-adenosyl-L-methionine (AdoMet) was determined, showing that it is a homodimer belonging to the SpoU family within the SPOUT class of methyltransferases. The relationships within this class were analyzed in detail and, in addition, a novel fourth SpoU sequence fingerprint is proposed. Each subunit of AviRb consists of two domains. The N-terminal domain, being related to the ribosomal proteins L30 and L7Ae, is likely to bind RNA. The C-terminal domain is related to all SPOUT methyltransferases, and is responsible for AdoMet-binding, catalysis and dimerization. The cofactor binds at the characteristic knot of the polypeptide in an unusually bent conformation. The transferred methyl group points to a broad cleft formed with the L30-type domain of the other subunit. Measurements of mutant activity revealed four important residues responsible for catalysis and allowed the modeling of a complex between AviRb and the RNA target. The model includes a specificity pocket for uracil but does not contain a base for deprotonating the 2'-O atom of U2479 on methylation.


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Last modification of this entry: Sept. 6, 2012