The mCpG-binding domain of human MBD3 does not bind to mCpG but interacts with NuRD/Mi2 components HDAC1 and MTA2.
Although mammalian MBD3 contains the mCpG-binding domain (MBD) and is highly homologous with the authentic mCpG-binding protein MBD2, it was reported that the protein does not bind to mCpG specifically. Using recombinant human wild type and mutant MBD3 proteins, we demonstrated that atypical amino acids found in MBD3 MBD, namely, His-30 and Phe-34, are responsible for the inability of MBD3 to bind to mCpG. Interestingly, although H30K/F34Y MBD3 mutant protein binds to mCpG efficiently in vitro, it was not localized at the mCpG-rich pericentromeric regions in mouse cells. We also showed that Y34F MBD2b MBD, which possesses not the mCpG-specific DNA-binding activity but the nonspecific DNA-binding activity, was localized at the pericentromeric regions. These results suggested that the mCpG-specific DNA-binding activity is largely dispensable, and another factor(s) is required for the localization of MBD proteins in vivo. MBD3 was identified as a component of the NuRD/Mi2 complex that shows chromatin remodeling and histone deacetylase activities. We demonstrated that MBD3 MBD is necessary and sufficient for binding to HDAC1 and MTA2, two components of the NuRD/Mi2 complex. It was therefore suggested that mCpG-binding-defective MBD3 has evolutionarily conserved its MBD because of the secondary role played by the MBD in protein-protein interactions.
Saito
Motoki
M
Laboratory of Molecular and Cellular Assembly, Department of Biological Information, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.
Ishikawa
Fuyuki
F
D000595:Amino Acid Sequence; D020137:Base Pair Mismatch; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D018899:CpG Islands; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012097:Repressor Proteins; D014157:Transcription Factors
D002352:Carrier Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; C115369:MBD3 protein, human; C492013:Mbd3 protein, mouse; D012097:Repressor Proteins; D014157:Transcription Factors; C120917:MTA2 protein, human; C110550:HDAC1 protein, human; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases