Posttranslational modifications (PTMs) play a crucial role in a wide range of biological processes. Lysine crotonylation (Kcr) is a newly discovered histone PTM that is enriched at active gene promoters and potential enhancers in mammalian cell genomes. However, the cellular enzymes that regulate the addition and removal of Kcr are unknown, which has hindered further investigation of its cellular functions. Here we used a chemical proteomics approach to comprehensively profile ‘eraser’ enzymes that recognize a lysine-4 crotonylated histone H3 (H3K4Cr) mark. We found that Sirt1, Sirt2, and Sirt3 can catalyze the hydrolysis of lysine crotonylated histone peptides and proteins. More importantly, Sirt3 functions as a decrotonylase to regulate histone Kcr dynamics and gene transcription in living cells. This discovery not only opens opportunities for examining the physiological significance of histone Kcr, but also helps to unravel the unknown cellular mechanisms controlled by Sirt3, that have previously been considered solely as a deacetylase.

This Feature Article summarizes our efforts in developing a new family of foldamers from α-, β- and γ-aminoxy acids. From a series of conformational studies, we demonstrate that peptides consisting of aminoxy acids adopt several well-defined secondary structures, such as α N–O turns (which feature an eight-membered-ring hydrogen bond), β N–O turns (a nine-membered-ring hydrogen bond), γ N–O turns (a ten-membered-ring hydrogen bond), 1.8₈ helices (consecutive homochiral α N–O turns), 7/8 helices (alternating α N–O turns and γ-turns), 1.7₉ helices (consecutive β N–O turns), reverse turns (consecutive heterochiral α N–O turns) and sheet-like structures.