Butyrate blocks specific histone acetylation by preventing recruitment of p300 to acetylated histones

Butyrate, a short-chain fatty acid (SCFA) produced by microbial fermentation of dietary fiber, exerts beneficial metabolic and immunomodulatory functions through hyperactivation of the histone acetylase (HAT) p300 and inhibition of histone deacetylases (HDAC). These effects are widely believed to result in the acetylation of distinct histones that regulate specific genes, including at transcription starting sites (TSS) and enhancers. However, we show that this is not the case, as butyrate dose-dependently increases the acetylation of histones throughout the entire genome. Molecular dynamics simulations suggest that the RING-loop prevents the recruitment of p300 to acetylated histones through its bromodomain, and thereby cannot maintain the acetylation of specific histones through positive feedback. This was confirmed by showing that only catalytically inactive p300 stably binds to acetylated histones. Thus, the epigenetic regulation of specific genes by butyrate is limited, but butyrate instead increases histone acetylation globally resulting in opening of the entire chromatin structure.