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.

Highlights d H4K91glu is a new histone mark enriched at promoters of highly expressed genes d H4K91glu destabilizes nucleosome by affecting (H2A/H2B) and (H3/H4) 2 interaction d H4K91glu is regulated by KAT2A and Sirt7 as its ''writer'' and ''eraser,'' respectively d H4K91glu regulates chromatin structure and dynamics in response to DNA damage

Post-translational modifications (PTMs) have key roles in regulating protein-protein interactions in living cells. However, it remains a challenge to identify these PTM-mediated interactions. Here we develop a new lysine-based photo-reactive amino acid, termed photo-lysine. We demonstrate that photo-lysine, which is readily incorporated into proteins by native mammalian translation machinery, can be used to capture and identify proteins that recognize lysine PTMs, including 'readers' and 'erasers' of histone modifications.

Tag! You′re it! MalAM‐yne is a chemical reporter for malonylation of lysines within proteins (see scheme), a newly identified posttranslational modification. MalAM‐yne is cell‐permeable and metabolically incorporated into proteins in living cells. Subsequent bioorthogonal tag conjugation allows the fluorescent visualization of cellular malonylation and profiling of malonylated proteins.

Highlights d ADdis-Cys allows comprehensive identification of (non) histone PTM ''readers'' d ADdis-Cys enables mapping of binding regions of PTM readers d ADdis-Cys helps ''visualizing'' binding sites in intrinsically disordered domains d ADdis-Cys identifies human C1QBP as a histone H3-H4 chaperone

Posttranslational modifications of histones play key roles in the dynamic regulation of chromatin structure. Lysine succinylation is a new type of histone modification, but its biological significance in chromatin structure and dynamics remains unknown. Here we develop a chemical approach to site-specifically install a succinyl lysine analog into histones. This analog serves as an ideal structural and functional mimic to natural succinyl lysine. The incorporation of this succinylation mimic into histone H2B at lysine 34, a succinylation site at the nucleosomal DNA-histone interface, leads to significant decrease in nucleosome stability in vitro, which is consistent with the defects in chromatin structure of a budding yeast strain containing a lysine-to-glutamate mutation at the corresponding residue of yeast histone H2B. This study provides a simple method for the rapid generation of histones with site-specific succinylation mimics, and reveals novel regulatory mechanisms of histone succinylation in the dynamic organization of chromatin.

Posttranslational modifications (PTMs) of lysine are crucial histone marks that regulate diverse biological processes. The functional roles and regulation mechanism of many newly identified lysine PTMs, however, remain yet to be understood. Here we report a photoaffinity crotonyl lysine (Kcr) analogue that can be genetically and site-specifically incorporated into histone proteins. This, in conjunction with the genetically encoded photo-lysine as a "control probe", enables the capture and identification of enzymatic machinery and/or effector proteins for histone lysine crotonylation.

For its effects on the development and progression of CIA and for its therapeutic effect on CIA, NK-007 has great potential to be a therapeutic agent for human rheumatoid arthritis.