Functional analysis of conserved motifs in EcoP15I DNA methyltransferase

Ahmad, Ishtiyaque and Rao, Desirazu N (1996) Functional analysis of conserved motifs in EcoP15I DNA methyltransferase. In: Journal of Molecular Biology, 259 (2). pp. 229-240.

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Abstract

EcoP15I DNA methyltransferase recognizes the sequence 5'-CAGCAG-3' and transfers a methyl group to N-6 of the second adenine residue in the recognition sequence. All N-6 adenine methyltransferases contain two highly conserved sequences, FxGxG (motif I), postulated to form part of the S-adenosyl-L-methionine binding site and (D/N/S)PP(Y/F) (motif IV) involved in catalysis. We have altered the second glycine residue in motif I to arginine and serine, and substituted tyrosine in motif IV with tryptophan in EcoP15I DNA methyltransferase, using site-directed mutagenesis. The mutant enzymes were overexpressed, purified and characterized by biochemical methods. The mutations in motif I completely abolished AdoMet binding but left target DNA recognition unaltered. Although the mutation in motif IV resulted in loss of enzyme activity, we observed enhanced crosslinking of S-adenosyl-L-methionine and DNA. This implies that DNA and AdoMet binding sites are close to motif IV. Taken together, these results reinforce the importance of motif I in AdoMet binding and motif IV in catalysis. Additionally, limited proteolysis and UV crosslinking experiments with EcoP15I DNA methyltransferase imply that DNA binds in a cleft formed by two domains in the protein. Methylation protection analysis provides evidence for the fact that EcoP15I DNA MTase makes contacts in the major groove of its substrate DNA. Interestingly, hypermethylation of the guanine residue next to the target adenine residue indicates that the protein probably flips out the target adenine residue. (C) 1996 Academic Press Limited

Item Type:	Journal Article
Publication:	Journal of Molecular Biology
Publisher:	Elsevier science
Additional Information:	Copyright of this article belongs to Elsevier science.
Keywords:	type III restriction-modification system;site-directed mutagenesis;sinefungin;DNA-protein crosslinking
Department/Centre:	Division of Chemical Sciences > Organic Chemistry
Date Deposited:	28 Apr 2011 05:12
Last Modified:	28 Apr 2011 05:12
URI:	http://eprints.iisc.ac.in/id/eprint/37250

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