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(a) The chemical structure of acetyl coenzyme A. The characteristic sharp bend observed in the bound forms of AcCoA and CoA in GNAT superfamily members is around the bond highlighted by the starred carbon atoms. (b) The general reaction catalyzed by GCN5-related N-acetyltransferases, showing the presumed tetrahedral intermediate that results from nucleophilic attack of a primary amine on the acyl carbon of the acetyl group.

Alignment of the three-dimensional structures of GCN5-related N-acetyltransferases. AANAT, serotonin N-acetyltransferase; PCAF, p300/CBP-associating factor; yHat, histone N-acetyltransferase; AAC, aminoglycoside N-acetyltransferase. For AANAT (a), the complex with the bisubstrate analog is shown (indole ring in blue), while for tGCN5 (c), the ternary complex with CoA and an 11-residue peptide (in blue) is shown. The black lines indicate coenzyme A or acetyl coenzyme A. The four conserved motifs of the GNAT superfamily—C, D, A, and B—are shown in purple, green, yellow, and red, respectively. Structural elements that represent insertions into motifs C and B are shown in lilac and pink, respectively. Helix α1 of yHat1 is shown in blue to indicate the positional shift of this helix with respect to the other aligned structures. The figure was prepared using MOLSCRIPT (18).