Chromatin context-dependent deacetylation by the asymmetric Rpd3L

Area of Science:

• Molecular Biology
• Epigenetics
• Structural Biology

Background:

• Gene expression regulation depends on chromatin-associated complexes responding to epigenetic signals.
• The Sin3 histone deacetylase complex (Rpd3L) dynamically adapts to chromatin states for transcriptional silencing.
• Mechanisms of Rpd3L catalytic activation within chromatin remain poorly understood.

Purpose of the Study:

• To elucidate the structural basis of Rpd3L catalytic activation on nucleosome substrates.
• To uncover the substrate-guided mechanism of Rpd3L allosteric activation.
• To understand how Rpd3L interprets chromatin context for enzymatic regulation.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structure of Rpd3L bound to nucleosomes.
• Biochemical assays to assess Rpd3L activity and substrate specificity.
• Mass spectrometry to analyze Rpd3L interactions and modifications.

Main Results:

• Near-atomic resolution cryo-EM structure of Rpd3L bound to mono- and di-nucleosome substrates.
• Revealed an asymmetric Rpd3L architecture with dual nucleosome engagement.
• Demonstrated substrate-guided allosteric activation, enhancing catalytic activity and substrate specificity.

Conclusions:

• Rpd3L utilizes a hierarchical mechanism involving dual nucleosome binding for activation.
• The spatial arrangement of nucleosomes dictates Rpd3L enzymatic output at promoter regions.
• Provides a framework for understanding higher-order chromatin repression by regulatory complexes.