Investigation of the β-sheet interactions between dHP1 chromodomain and histone 3

Area of Science:

• Biochemistry
• Molecular Biology
• Epigenetics

Background:

• Histone methylation, specifically on lysine 9 of histone H3 (H3 K9Me), is a key epigenetic mark.
• Heterochromatin protein 1 (HP1) from Drosophila binds H3 K9Me via its chromodomain, leading to gene silencing.
• The binding involves an aromatic cage and the formation of a three-stranded β-sheet between the histone tail and the chromodomain.

Purpose of the Study:

• To investigate the sequence selectivity of the dHP1 chromodomain for the histone H3 tail.
• To explore how mutations affecting β-sheet interactions influence binding affinity.
• To compare these interactions with other model systems and statistical studies.

Main Methods:

• Site-directed mutagenesis of key residues in both the histone H3 tail (Thr6) and the dHP1 chromodomain (Ala25, Asp62).
• Amino acid substitutions focused on residues with high β-sheet propensity and favorable side chain-side chain interactions.
• Assessment of binding affinity between wild-type and mutant proteins.

Main Results:

• Approximately 50% of chromodomain mutants exhibited equal or enhanced binding to the histone tail.
• Around 25% of histone tail mutants demonstrated tighter binding compared to the native sequence.
• Mutations impacting β-sheet interactions significantly altered binding selectivity.

Conclusions:

• The study provides novel insights into the sequence selectivity of dHP1 chromodomain-histone tail interactions.
• Findings highlight the importance of β-sheet-mediated protein-protein interactions.
• The results suggest the feasibility of designing specific histone-chromodomain pairs for chemical biology tools.