BAH: Owing to extensive intermolecular contacts, the ankyrin repeats of G9a and GLP and the BAH domain of ORC1 show high specificity for di- or monomethylated H3K9 and H4K20me2, respectively. The H3K9me2 peptide is sandwiched between the β-turns and α-helices of the fourth and fifth ankyrin repeats, whereas K9me2 fits into the aromatic cage also containing a glutamate. (1)
Reference
1. Musselman CA, Lalonde ME, Cote J, Kutateladze TG.Perceiving the epigenetic landscape through histone readers. Nat Struct Mol Biol.2012;19(12):1218-27. PMID: 23211769.
Chromodomain: The chromodomain is the smallest member, consisting of four curved β-strands and an α-helix. The chromodomains of HP1 and Polycomb were found to recognize histone H3 trimethylated at K9 (H3K9me3) and H3K27me3, respectively, and these proteins were the first examples of readers specific for methyllysine. Chromodomains generally prefer trimethylated lysine, though some have been shown to bind dimethylated species. The aromatic cage of the chromodomain of mouse and fly HP1 contains an aspartate or glutamate residue, accounting for its ability to interact well with H3K9me3 and dimethylated H3K9 (H3K9me2). (1)
Reference
1. Musselman CA, Lalonde ME, Cote J, Kutateladze TG.Perceiving the epigenetic landscape through histone readers. Nat Struct Mol Biol.2012;19(12):1218-27. PMID: 23211769.
DCD: In the double chromodomain (DCD), both chromodomains share their general secondary structure elements with those previously seen in HP1 and Polycomb chromodomains. The linker segment forms a novel helix–turn–helix structure that juxtaposes the two chromodomains to form a continuous surface. A total of 350 Å is buried at the interface of these tandem chromodomains. (1)
Reference
1. John F. Flanagan, Li-Zhi Mi, Maksymilian Chruszcz, Marcin Cymborowski, Katrina L. Clines, Youngchang Kim, Wladek Minor, Fraydoon Rastinejad & Sepideh Khorasanizadeh.Double chromodomains cooperate to recognize the methylated histone H3 tail. Nature.2005;438:1181–1185. PMID: 16372014.