Structural insight into histone recognition by the ING PHD fingers.

Area of Science:

• Molecular Biology
• Epigenetics
• Cancer Biology

Background:

• Inhibitor of Growth (ING) proteins are tumor suppressors involved in DNA repair, senescence, and apoptosis.
• ING proteins feature unique N-terminal domains and a C-terminal plant homeodomain (PHD) finger.
• The PHD finger specifically recognizes histone H3 trimethylated at lysine 4 (H3K4me3).

Purpose of the Study:

• To elucidate the molecular mechanism of H3K4me3 recognition by ING PHD fingers.
• To analyze determinants of histone specificity and compare ING PHD finger structures and activities.
• To understand the role of ING proteins in regulating chromatin acetylation and their link to tumorigenesis.

Main Methods:

• Structural analysis of ING PHD fingers complexed with H3K4me3 peptides at atomic resolution.
• Detailed examination of intermolecular interactions, including hydrogen bonds, hydrophobic, and cation-pi contacts.
• Comparative analysis of structural and functional subsets of ING PHD fingers.

Main Results:

• ING PHD fingers bind H3K4me3 in a large surface site, involving extensive interactions with the first six residues of the histone tail.
• Specific binding is dictated by conserved aromatic/hydrophobic residues forming grooves for trimethylated Lys4 and Arg2, and a narrow channel.
• ING proteins act as molecular tethers, connecting HDAC and HAT complexes to chromatin, thereby regulating acetylation.

Conclusions:

• The precise structural interactions of ING PHD fingers with H3K4me3 are key to their specificity and function.
• ING proteins play a critical role in chromatin regulation by bridging epigenetic modifying enzymes.
• Understanding these mechanisms provides insight into the biological and tumorigenic activities of ING tumor suppressors.