Human Class I histone deacetylase complexes show enhanced catalytic activity in the presence of ATP and co-immunoprecipitate with the ATP-dpendent chaperone protein Hsp70

Antibodies to histone deacetylases (HDACs) have been used to immuno-isolate deacetylase complexes from HeLa cell extracts. Complexes shown to contain HDAC I, HDAC3, HDAC6, and HDAC1+2 as their catalytic subunits have been used in an antibody-based assay that detects deacetylation of whole histories at defined lysines. The class 11 deacetylase HDAC6 was inactive in this assay, but the three class I enzymes deacetylated all histone lysines tested, although with varying efficiency. In comparison to HDAC1, HDAC3 preferentially deacetylated lysines 5 and 12 of H4 and lysine 5 of H2A. H4 tails in purified mononucleosomes were refractory to deacetylation by both HDAC1 and HDAC3, unless ATP was added to the reaction mix. Surprisingly, ATP a so consistently enhanced cleavage of free, non-nucleosomal histones, but not small peptides, by both enzyme complexes. We found no evidence that ATP operates by phosphorylation of components of the HDAC complex but have shown that HDACs 1, 2, and 3 all co-immunoprecipitate with the ATP-dependent chaperone protein Hsp70. Another common ATP-dependent chaperone, Hsp90, was absent from all HDAC complexes tested, whereas Hsp60 associated with HDAC1 only. We suggest that Hsp chaperone proteins enhance the deacetylase activity of HDAC complexes by ATP-dependent manipulation of protein substrates.