Lysine acetyltransferases (KATs), p300 (KAT3B), and its close homologue CREB-binding protein (KAT3A) are probably the most widely studied KATs with well documented roles in various cellular processes. Hence, the dysfunction of p300 may result in the dysregulation of gene expression leading to the manifestation of many disorders. The acetyltransferase activity of p300/CREB-binding protein is therefore considered as a target for new generation therapeutics. We describe here a natural compound, plumbagin (RTK1), isolated from Plumbago rosea root extract, that inhibits histone acetyltransferase activity potently in vivo. Interestingly, RTK1 specifically inhibits the p300-mediated acetylation of p53 but not the acetylation by another acetyltransferase, p300/CREB-binding protein -associated factor, PCAF, in vivo. RTK1 inhibits p300 histone acetyltransferase activity in a noncompetitive manner. Docking studies and site-directed mutagenesis of the p300 histone acetyltransferase domain suggest that a single hydroxyl group of RTK1 makes a hydrogen bond with the lysine 1358 residue of this domain. In agreement with this, we found that indeed the hydroxyl group-substituted plumbagin derivatives lost the acetyltransferase inhibitory activity. This study describes for the first time the chemical entity (hydroxyl group) required for the inhibition of acetyltransferase activity.

Dysfunction of histone acetyltransferases (HATs) leads to several diseases including cancer, diabetes, and asthma. Therefore, small molecule inhibitors and activators of HATs are being considered as new generation therapeutics. Here, we report the molecular mechanisms of p300 HAT inhibition by specific and nonspecific HAT inhibitors: garcinol, isogarcinol, and 1 (LTK14). The p300 specific HAT inhibitor 1 behaves as a noncompetitive inhibitor for both acetyl-CoA and histone, unlike nonspecific HAT inhibitors garcinol and isogarcinol. The isothermal calorimetric data suggest that there is a high affinity enthalpy driven single binding site for 1 on p300HAT domain in contrast to two binding sites for garcinol and isogarcinol. Furthermore, the precise nature of molecular interactions was determined by using fluorescence, docking, and mutational studies. On the basis of these observations, we have proposed the mechanisms of specific versus nonspecific HAT inhibition by these small molecule compounds, which may be useful to design therapeutically favorable HAT inhibitors.