The Methyl-CpG-binding domain (MBD) in molecular biology binds to DNA that contains one or more symmetrically methylated CpGs. MBD has negligible non-specific affinity for unmethylated DNA. In vitro foot-printing with the chromosomal protein MeCP2 showed that the MBD could protect a 12 nucleotide region surrounding a methyl CpG pair. The structure of the MBD domain bound to methylated DNA has been solved (PDB: 3C2I​). It recognizes the hydration of the major groove at methylated sites.