3tpz | pdb_00003tpz
2.1 Angstrom crystal structure of the L114P mutant of E. Coli KsgA
Structural highlights
Function[RSMA_ECOLI] Specifically dimethylates two adjacent adenosines (A1518 and A1519) in the loop of a conserved hairpin near the 3'-end of 16S rRNA in the 30S particle. May play a critical role in biogenesis of 30S subunits. Has also a DNA glycosylase/AP lyase activity that removes C mispaired with oxidized T from DNA, and may play a role in protection of DNA against oxidative stress.[1] [2] [3] Publication Abstract from PubMedThe KsgA methyltransferase is universally conserved and plays a key role in regulating ribosome biogenesis. KsgA has a complex reaction mechanism, transferring a total of four methyl groups onto two separate adenosine residues, A1518 and A1519, in the small subunit rRNA. This means that the active site pocket must accept both adenosine and N(6)-methyladenosine as substrates to catalyze formation of the final product N(6),N(6)-dimethyladenosine. KsgA is related to DNA adenosine methyltransferases, which transfer only a single methyl group to their target adenosine residue. We demonstrate that part of the discrimination between mono- and dimethyltransferase activity lies in a single residue in the active site, L114; this residue is part of a conserved motif, known as motif IV, which is common to a large group of S-adenosyl-l-methionine-dependent methyltransferases. Mutation of the leucine to a proline mimics the sequence found in DNA methyltransferases. The L114P mutant of KsgA shows diminished overall activity, and its ability to methylate the N(6)-methyladenosine intermediate to produce N(6),N(6)-dimethyladenosine is impaired; this is in contrast to a second active site mutation, N113A, which diminishes activity to a level comparable to L114P without affecting the methylation of N(6)-methyladenosine. We discuss the implications of this work for understanding the mechanism of KsgA's multiple catalytic steps. Control of Substrate Specificity by a Single Active Site Residue of the KsgA Methyltransferase.,O'Farrell HC, Musayev FN, Scarsdale JN, Rife JP Biochemistry. 2012 Jan 10;51(1):466-74. Epub 2011 Dec 22. PMID:22142337[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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