Structural analysis of lysine-4 methylated histone H3 proteins using synchrotron radiation circular dichroism spectroscopy.

We report structural alterations of histone H3 proteins induced by lysine-4 (K4) monomethylation, dimethylation, and trimethylation identified by using synchrotron radiation circular dichroism spectroscopy. Compared with unmethylated H3, monomethylation and dimethylation induced increases in α-helix structures and decreases in β-strand structures. In contrast, trimethylation decreased α-helix content but increased β-strand content. The structural differences among K4-unmethylated/methylated H3 may allow epigenetic enzymes to discriminate the substrates both chemically and sterically.