Multivalent Interactions by the Set8 Histone Methyltransferase With Its Nucleosome Substrate.

Area of Science:

• Biochemistry
• Molecular Biology
• Epigenetics

Background:

• Set8 is the sole mammalian enzyme catalyzing H4K20me1, a vital epigenetic mark for maintaining genomic stability in eukaryotic cells.
• Understanding the mechanism of Set8-nucleosome interaction is key to comprehending epigenetic regulation.

Purpose of the Study:

• To elucidate the structural basis of Set8's nucleosome binding and methylation activity.
• To investigate the role of different Set8 domains, including its N-terminal extension, in nucleosome interaction.

Main Methods:

• Crystallographic studies of the Set8/nucleosome complex.
• Solution studies of the Set8/nucleosome complex.
• Biochemical assays to assess protein-protein interactions.

Main Results:

• Set8 utilizes its i-SET and c-SET domains to bind nucleosomal DNA, positioning the SET domain for H4 Lys20 methylation.
• A basic N-terminal extension of Set8 plays a significant role in nucleosome binding, potentially via interaction with the H2A/H2B acidic patch.
• Proliferating cell nuclear antigen (PCNA) and the nucleosome compete for Set8 binding through this N-terminal extension.

Conclusions:

• Set8 employs a multivalent binding strategy involving DNA, histone residues, and its N-terminal extension for efficient nucleosome recognition and catalysis.
• The competitive binding of PCNA and nucleosomes to Set8's N-terminal extension provides a mechanism for regulating Set8 activity and stability during the cell cycle.