Histone lysine acylations play an important role in the regulation of gene transcription in chromatin. Unlike histone acetyl-lysine, molecular recognition of a recently identified crotonyl-lysine mark is much less understood. Here, we report that the YEATS domain of AF9 preferentially binds crotonyl-lysine over acetyl-lysine in histone H3. Nuclear magnetic resonance structural analysis reveals that crotonyl-lysine of histone H3 lysine 18 is engulfed deep in an aromatic cage of the YEATS domain where the carbonyl oxygen of crotonyl-lysine forms a hydrogen bond with the backbone amide of protein residue Tyr78. The crotonyl-lysine, through its unique electron-rich double-bond side chain, engages π-π aromatic stacking and extended hydrophobic/aromatic interactions with the YEATS domain compared with acetyl-lysine. Our mutational analysis confirmed key protein residues Phe59 and Tyr78 for crotonyl-lysine recognition. Importantly, our findings present a new structural mechanism of protein-protein interactions mediated by histone lysine crotonylation, and show how the cells interpret acyl-lysine marks in different biological contexts.
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