A single amino acid substitution confers enhanced methylation activity of mammalian Dnmt3b on chromatin DNA.
Dnmt3a and Dnmt3b are paralogous enzymes responsible for de novo DNA methylation but with distinguished biological functions. In mice, disruption of Dnmt3b but not Dnmt3a causes global DNA hypomethylation, especially in repetitive sequences, which comprise the large majority of methylated DNA in the genome. By measuring DNA methylation activity of Dnmt3a and Dnmt3b homologues from five species, we found that mammalian Dnmt3b possessed significantly higher methylation activity on chromatin DNA than Dnmt3a and non-mammalian Dnmt3b. Sequence comparison and mutagenesis experiments identified a single amino acid substitution (I662N) in mammalian Dnmt3b as being crucial for its high chromatin DNA methylation activity. Further mechanistic studies demonstrated this substitution markedly enhanced the binding of Dnmt3b to nucleosomes and hence increased the chromatin DNA methylation activity. Moreover, this substitution was crucial for Dnmt3b to efficiently methylate repetitive sequences, which increased dramatically in mammalian genomes. Consistent with our observation that Dnmt3b evolved more rapidly than Dnmt3a during the emergence of mammals, these results demonstrated that the I662N substitution in mammalian Dnmt3b conferred enhanced chromatin DNA methylation activity and contributed to functional adaptation in the epigenetic system.
Laboratory of Molecular Cell Biology and Center of Cell Signaling, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, PR China.
Li
L
Shen
Ge
G
Gao
Ying
Y
Zhang
He
H
Zhang
Zhiqiang
Z
Ye
Shichao
S
Huang
Jinyan
J
Huang
Jiuhong
J
Kang
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002478:Cells, Cultured; D002843:Chromatin / Q000201:enzymology*; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D019175:DNA Methylation; D000090205:DNA Methyltransferase 3A; D044127:Epigenesis, Genetic; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009707:Nucleosomes / Q000201:enzymology; D011485:Protein Binding; D012091:Repetitive Sequences, Nucleic Acid; D000097584:DNA Methyltransferase 3B
D002843:Chromatin; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A; D009707:Nucleosomes; D000097584:DNA Methyltransferase 3B; C000717967:DNMT3A protein, human; C000715535:Dnmt3a protein, mouse