Abstract
Gcn5 is a conserved acetyltransferase that regulates transcription by acetylating the N-terminal tails of histones. Motivated by recent studies identifying a chemically diverse array of lysine acyl modifications in vivo, we examined the acyl chain specificity of the acetyltransferase, human Gcn5 (Gcn5L2). Whereas Gcn5L2 robustly catalyzes lysine acetylation, the acyltransferase activity of Gcn5L2 gets progressively weaker with increasing acyl chain length. To understand how Gcn5 discriminates between different acyl-CoA molecules, we determined structures of the catalytic domain of human Gcn5L2 bound to propionyl-CoA and butyryl-CoA. Although the active site of Gcn5L2 can accommodate propionyl-CoA and butyryl-CoA without major structural rearrangements, butyryl-CoA adopts a conformation incompatible with catalysis that obstructs the path of the incoming lysine residue and acts as a competitive inhibitor for Gcn5L2 versus acetyl-CoA. These structures demonstrate how Gcn5L2 discriminates between acyl chain donors and explain why Gcn5L2 has weak activity for acyl moieties that are larger than an acetyl group.
