Figure 3. SIRT3 binds to and deacetylates CypD at K166. (A) CypD-K166 lies adjacent to the CsA binding pocket (Protein Data Bank, 2Z6W). (B)Interaction studies using HA-tagged SIRT3, SIRT4 and SIRT5 and FLAG-tagged CypD assessed by coimmunoprecipitation. (C) Specificity of a polyclonal antibody raised against acetylated CypD-K166 confirmed by a lack of Western blot signal for mutant CypD-K166R. SIRT3 and SIRT3-H248Y were co-transfected with FLAG-tagged CypD and the level of acetylation at CypD-K166 was assessed. (D) Vectors for FLAG-tagged SIRT3 and SIRT3-H248Y transfected in HEK 293T cells were immunoprecipitated, then incubated with purified CypD in the presence of the SIRT3 co-substrate NAD+.