The solution structure of the domain from MeCP2 that binds to methylated DNA

MeCP2 is an abundant mammalian protein that binds methylated CpG (mCpG) seq uences within double-stranded DNA, represses transcription by recruiting hi stone deacetylases, and is essential for embryonic development. It is one o f a family of proteins which mediate the biological consequences of DNA met hylation. These proteins each possess a sequence motif of about 70 residues which, in MeCP2, form a domain necessary and sufficient for binding to mCp G. The solution structure of the mCpG-binding domain (MBD) from MeCP2 has b een solved and the DNA-binding surface of the domain mapped using NMR spect roscopy. Residues 95-162 of MeCP2 adopt a novel fold forming a wedge-shaped structure. An N-terminal four-stranded antiparallel beta-sheet forms one f ace of the wedge, while the other face is formed mainly by a C-terminal hel ical region. The thin end of the wedge is extended by a long loop between b eta-strands B and C containing many basic residues. The B-C loop together w ith residues in strands B, C and D, and at the N terminus of the alpha-heli x, appears to form an interface with methylated DNA. Unstructured residues at the NH2 terminus of the domain are also involved in formation of the com plex. The presence of numerous arginine and lysine side-chains on the DNA-b inding surface of MBD is consistent with the requirement for the mCpG site to be flanked by non-specific sequences of base-pairs. The absence of symme try in the domain implies that recognition does not exploit the symmetry of the binding site. A conserved hydrophobic pocket containing the side-chain s of Tyr123 and Ile125 on the positively charged beta-sheet face is a candi date for the region of contact with the methyl-groups of the modified cytos ine residues. (C) 1999 Academic Press.