Complex Structure And Function Of Histone Acetyltransferase And Adenovirus E1A

p300/CBP and p300/CBP associated factor (PCAF, also known as KAT2B for lysine acetyltransferase2B) are histone acetyltransferase (HAT), which acetylate histones and nonhistone proteins to regulate transcriptions of specific sets of genes. Like the most classical transcriptional coactivators, p300/CBP and PCAF can also bridge the transcriptional factors to the basal transcriptional complex to enhance the appropriate activities of genes during various physiological processes, such as cell cycle, apoptosis, and carcinogenesis.The structures of PCAF/Gcn5HAT domains have been solved in the last decade. Here we have found that PCAF acetyltransferase (HAT) domain forms two dimeric structures that have not been previously described. Its dimerizations are mediated by either four-helical hydrophobic interactions or α β-sheet extension. The mutations in PCAF HAT domain that disrupt one or both interfaces decreases PCAF dimerization as shown in our chemical crosslinking experiments, consistent with our structural observations. Our pulldown, static light scattering and dynamic light scattering data further indicate that PCAF HAT may exist as a dimer in solution when at proper concentration. We have also found that wt HAT has slightly better Kcat than those PCAF mutants, suggesting that the dimeration of PCAF may play a role in enzymatic efficiency. In summary, our series of experiments implicate that PCAF HAT domain is able to form a dimer in solution.Adenoviral oncoprotein El A has four motifs, including N terminus (EN). CR1, CR2and CR3. A fragment of the first60amino acid residues, which has EN and CR1motifs, has been shown to directly interact with PCAF and p300/CBP Cysteine-Histidine rich domain (CH3). We demonstrate that the EN and CR1motifs can independently interact with PCAF and p300while EN is significantly stronger binder. For the CR1a complete motif is required for the maximal PCAF binding. The EN and CR1can both bind to p300CH3domain more efficiently than PCAF HAT. In Vitro acetylation assay shows that EN and CR1can also independently stimulate the acetyltransferase activity of PCAF on histone H3. and the PCAF dimeric state is important for E1A regulation. Taken together, these data suggest that the EN and CR1motifs can independently interact with PCAF and p300. and the acetyltransferase activity of PCAF may be regulated by the dimerization of HAT domain and the viral protein E1A.In summary, the analyses of PCAF HAT and E1A complex or p300and E1A complex structures have furthered our understanding on the interactions of E1A with PCAF and p300, in particular on regulations of E1A to PCAF/Gcn5histone acetyltransferase activity. We are actively working on crystal structures of these complexes, which may provide solid structural bases for inhibitor designs to target p300/CBP and PCAF/Gcn5molecules in cells.