title: Structure and function of the antibiotic resistance-mediating methyltransferase AviRb from Streptomyces viridochromogenes.
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.
authors.affiliation: Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstr. 21, D-79104 Freiburg im Breisgau, Germany.
authors.forename: Tanja G
authors.initials: TG
authors.lastname: Mosbacher
authors.forename: Andreas
authors.initials: A
authors.lastname: Bechthold
authors.forename: Georg E
authors.initials: GE
authors.lastname: Schulz
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D004351:Drug Resistance; D008780:Methyltransferases / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D013302:Streptomyces / Q000201:enzymology*; D013329:Structure-Activity Relationship
chemical_list: D008780:Methyltransferases