L3MBTL1(3xMBT) recognizes p53 monomethylated at lysine 382 (p53K382me1) in vitro. A, sequence alignment of the H4 N terminus and p53 C-terminal tail. Homology surrounding the SET8/53BP1 binding site is highlighted. Asterisks indicate methylation sites. B, L3MBTL1(3xMBT) binds to p53K382me1 and p53K382me2 peptides. Shown are the results from Western analysis of peptide pull-down assays with the indicated biotinylated peptides and GST-L3MBTL1(3xMBT). C, dissociation constants (Kd) of p53 or histone H4 peptides for L3MBTL1(3xMBT) were determined by ITC. Kd of H4K20me1 is shown as control. D, L3MBTL1(3xMBT) repeats are shown as a solid surface with the residues comprising the p53K382me1-binding pocket of MBT2 labeled and colored orange, brown, and yellow for aromatic, acidic, and hydrophobic/polar residues, respectively. Lysine 382me1 of the p53K382me1 peptide is shown as a stick model with C, O, and N atoms colored green, red, and blue, respectively. The unoccupied semi-aromatic pockets MBT1 and MBT3 are colored gray. E, close-up view of the K382me1 binding cage. A dotted red line depicts the hydrogen bond between the methylammonium proton and the carboxyl group of Asp-355. F, point mutations in the MBT2 repeat of L3MBTL1 abolish the p53K382me1 binding activity of L3MBTL1(3xMBT) in vitro. Western analysis of the indicated GST-L3MBTL1(3xMBT) mutants in peptide pull-down assays are shown.