Tuning HP1α chromodomain selectivity for di- and trimethyllysine

Area of Science:

• Epigenetics and Molecular Biology
• Protein-Protein Interactions
• Structural Biology

Background:

• Histone lysine methylation (mono-, di-, tri-) regulates gene expression by recruiting effector proteins.
• Dysregulation of histone methylation is linked to cancer, driving research into effector protein inhibitors.
• Understanding effector protein selectivity for different methylation states is crucial for therapeutic development.

Purpose of the Study:

• To investigate the mechanism of selectivity for histone lysine methylation states by the HP1α chromodomain.
• To elucidate the role of specific amino acid residues, particularly E52, in differentiating between H3K9Me2 and H3K9Me3 binding.
• To provide insights for guiding the development of targeted cancer therapies.

Main Methods:

• Site-directed mutagenesis of the Drosophila HP1α chromodomain at residue E52 (E52F, E52I, E52V, E52D, E52Q).
• Biochemical assays to measure binding affinities of wild-type and mutant proteins to dimethylated (H3K9Me2) and trimethylated (H3K9Me3) peptides.
• Comparative analysis of binding data to determine the impact of mutations on selectivity.

Main Results:

• The HP1α chromodomain binds H3K9Me2 and H3K9Me3 with similar affinities.
• Mutating E52 to glutamine (E52Q) significantly enhanced selectivity for H3K9Me3 over H3K9Me2.
• The E52Q mutant showed 3.5-fold weaker binding to H3K9Me2 (KD=52 μM) compared to H3K9Me3 (KD=15 μM).

Conclusions:

• Electrostatic interactions and hydrogen bonding at residue E52 are critical for differentiating histone methylation states.
• The findings offer a mechanistic understanding of methylation state recognition by effector proteins.
• This study provides valuable information for the rational design of inhibitors targeting cancer-associated epigenetic pathways.