Secondary Structures of Histone H3 Proteins with Unmethylated and Methylated Lysine-4 and -9 Residues: Characterization Using Circular Dichroism Spectroscopy

Abstract

Circular dichroism (CD) spectroscopy, especially that using synchrotron radiation as a light source, is a powerful tool for analyzing secondary structures of proteins in solution. In particular, CD spectroscopy allows observations of structural changes following post-translational modifications, such as methylation. In this chapter, techniques and measurement protocols are introduced. Recent structural analyses of H3 proteins before and after methylation of lysine-4 and -9 residues are also shown. In these CD spectroscopy analyses, mono- and dimethylation of H3 increased the presence of α-helical structures and decreased β-strand contents, whereas trimethylation decreased α-helix and increased β-strand contents. These structural alterations occurred at adjacent and distant residues from the methylated site.