HP1 Chromodomain: The perfect cap for H3K9me3

sketchfab

Post-translational modifications on histone protein tails significantly impact gene expression. Specifically, methylation of lysine residues at position 9 on histone H3 proteins (H3K9) serves as a defining indicator of inactive genes. To prevent unwanted gene expression in cells, it's essential to preserve this gene silencing by safeguarding specific methylated H3K9 sites from demethylation. The heterochromatin protein 1 (HP1) provides protection by recognizing and binding to trimethylated H3K9 (H3K9me3), blocking access to these sites for demethylases. Without HP1, H3K9me3 can be rapidly demethylated and then acetylated, leading to gene activation. The model depicted illustrates a structural breakdown of the functional region of HP1 known as the 'chromodomain'. Key residues within the chromodomain are able to recognize an essential motif surrounding the H3K9 residue, enabling high-affinity binding of its trimethylated state and protecting it from demethylation.