We have determined the solution NMR structure of SACOL2532, a putative GCN5-like N-acetyltransferase (GNAT) from Staphylococcus aureus. SACOL2532 was shown to bind both CoA and acetyl-CoA, and structures with and without bound CoA were determined. Based on analysis of the structure and sequence, a subfamily of small GCN5-related N-acetyltransferase (GNAT)-like proteins can be defined. Proteins from this subfamily, which is largely congruent with COG2388, are characterized by a cysteine residue in the acetyl-CoA binding site near the acetyl group, by their small size in relation to other GNATs, by a lack of obvious substrate binding site, and by a distinct conformation of bound CoA in relation to other GNATs. Subfamily members are found in many bacterial and eukaryotic genomes, and in some archaeal genomes. Whereas other GNATs transfer the acetyl group of acetyl-CoA directly to an aliphatic amine, the presence of the conserved cysteine residue suggests that proteins in the COG2388 GNAT-subfamily transfer an acetyl group from acetyl-CoA to one or more presently unidentified aliphatic amines via an acetyl (cysteine) enzyme intermediate. The apparent absence of a substrate-binding region suggests that the substrate is a macromolecule, such as another protein, or that a second protein subunit providing a substrate-binding region must combine with SACOL2532 to make a fully functional N-acetyl transferase.
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