The Acetylation Motif in AMP-Forming Acyl Coenzyme A Synthetases Contains Residues Critical for Acetylation and Recognition by the Protein Acetyltransferase Pat of Rhodopseudomonas palustris

The AMP-forming acyl coenzyme A (acyl-CoA) synthetases are a large class of enzymes found in both anabolic and catabolic pathways that activate fatty acids to acyl-CoA molecules. The protein acetyltransferase (Pat) from Rhodopseudomonas palustris (RpPat) inactivates AMP-forming acyl-CoA synthetases by acetylating the ε-amino group of a conserved, catalytic lysine residue. In all of the previously described RpPat substrates, this lysine residue is located within a PX₄GK motif that has been proposed to be a recognition motif for RpPat. Here, we report five new substrates for RpPat, all of which are also AMP-forming acyl-CoA synthetases. This finding supports the idea that Pat enzymes may have evolved to control the activity of this family of enzymes. Notably, RpPat did not acetylate the wild-type long-chain acyl-CoA synthetase B (RpLcsB; formerly Rpa2714) enzyme of this bacterium. However, a single amino acid change two residues upstream of the acetylation site was sufficient to convert RpLcsB into an RpPat substrate. The results of mutational and functional analyses of RpLcsB and RpPimA variants led us to propose PK/RTXS/T/V/NGKX₂K/R as a substrate recognition motif. The underlined positions within this motif are particularly important for acetylation by RpPat. The first residue, threonine, is located 4 amino acids upstream of the acetylation site. The second residue can be S/T/V/N and is located two positions upstream of the acetylation site. Analysis of published crystal structures suggests that the side chains of these two residues are very close to the acetylated lysine residue, indicating that they may directly interact with RpPat.