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Dissection of the DNA mimicry of the bacteriophage T7 Ocr protein using chemical modification.

TitleDissection of the DNA mimicry of the bacteriophage T7 Ocr protein using chemical modification.
Publication TypeJournal Article
Year of Publication2009
AuthorsStephanou AS, Roberts GA, Cooper LP, Clarke DJ, Thomson AR, C MacKay L, Nutley M, Cooper A, Dryden DTF
JournalJ Mol Biol
Volume391
Issue3
Pagination565-76
Date Published2009 Aug 21
ISSN1089-8638
KeywordsBacteriophage T7, Binding, Competitive, Dimerization, DNA, Methyltransferases, Molecular Mimicry, Nucleic Acid Conformation, Protein Folding, Viral Proteins
Abstract

The homodimeric Ocr (overcome classical restriction) protein of bacteriophage T7 is a molecular mimic of double-stranded DNA and a highly effective competitive inhibitor of the bacterial type I restriction/modification system. The surface of Ocr is replete with acidic residues that mimic the phosphate backbone of DNA. In addition, Ocr also mimics the overall dimensions of a bent 24-bp DNA molecule. In this study, we attempted to delineate these two mechanisms of DNA mimicry by chemically modifying the negative charges on the Ocr surface. Our analysis reveals that removal of about 46% of the carboxylate groups per Ocr monomer results in an approximately 50-fold reduction in binding affinity for a methyltransferase from a model type I restriction/modification system. The reduced affinity between Ocr with this degree of modification and the methyltransferase is comparable with the affinity of DNA for the methyltransferase. Additional modification to remove approximately 86% of the carboxylate groups further reduces its binding affinity, although the modified Ocr still binds to the methyltransferase via a mechanism attributable to the shape mimicry of a bent DNA molecule. Our results show that the electrostatic mimicry of Ocr increases the binding affinity for its target enzyme by up to approximately 800-fold.

DOI10.1016/j.jmb.2009.06.020
Alternate JournalJ. Mol. Biol.
PubMed ID19523474
PubMed Central IDPMC2806950
Grant ListB20089 / / Biotechnology and Biological Sciences Research Council / United Kingdom
BB/C511599/1 / / Biotechnology and Biological Sciences Research Council / United Kingdom
BB/D001870/1 / / Biotechnology and Biological Sciences Research Council / United Kingdom
C17860 / / Biotechnology and Biological Sciences Research Council / United Kingdom
GR080463MA / / Wellcome Trust / United Kingdom
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