Structural Studies of Histone Deacetylase Recruitment to the Sin3L/Rpd3L Corepressor Complex

Histone modifications play an important role in modulating chromatin dynamics with concomitant effects on gene expression. Acetylation of histone lysine residues is regulated by the opposing actions of histone acetylases (HATs) and deacetylases (HDACs). These enzymes are commonly found in large, multi-protein complexes and changes in expression or activity of HDACs are associated with multiple diseased states including cardiovascular disease. Nuclear HDACs, and in particular HDAC1 and 2, have been implicated in promoting cardiac hypertrophy. Despite considerable interest in HDACs as therapeutic targets, there is a significant gap in our knowledge about the structure and mechanism of action of these enzymes in the context of their respective complexes. The purpose of this proposed research is to clarify the molecular roles of conserved subunits in the HDAC1/2-containing Sin3L corepessor complex including Sin3, SAP30, and RbAp46/48. The role of Sin3 and SAP30 in HDAC1/2 recruitment will be investigated using structural and biochemical approaches to identify key interacting surfaces and determine their role in the regulation of HDAC1/2. This will include evaluation of inositol-1,4,5,6-tetraphospate as a modulator of HDAC activity. Additionally, structural studies of the RbAp46/48 – HDAC1/2 interaction will be used to clarify the function of the histone chaperone RbAp46/48 in the Sin3L complex. These studies will provide structural and mechanistic insights into the assembly and role of individual subunits in an important HDAC corepressor complex with implications for future isozyme and complex-specific drug discovery.