TABLE 7.
Different types of bacterial acyltransferases presented in this reviewa
| Enzyme type | Model enzyme(s) | Physiological function(s) | Reaction catalyzed | Acyl donor(s) | Acyl acceptor(s) | Catalytic site |
|---|---|---|---|---|---|---|
| WS/DGAT | AtfA from A. baylyi | WE and/or TAG storage | O-Acylation of (fatty) alcohol or DAG with acyl-CoA | Saturated or unsaturated acyl-CoAs (C2-C20; preferred, C16) | Linear alcohols (C2-C30; preferred, C14-C18); branched, cyclic, or aromatic alcohols; MAG or DAG, long-chain alkanediols, thiols, and dithiols; glycidol | HHxxxDG motif with catalytically active His |
| GPAT | PlsB from E. coli (but most bacteria have PlsY instead) | 1-Acylglycerol-3-phosphate (lysophosphatidate) synthesis | O-Acylation of sn-1 position of glycerol-3-phosphate with acyl-CoA or -ACP | C16 or C18:1 acyl-CoA or -ACP (PlsY, acylphosphate) | Glycerol-3-phosphate | HxxxxD motif catalytic dyad with catalytically active His (PlsY, catalytic His) |
| LPAAT | PlsC from E. coli | Phosphatidate synthesis | O-Acylation of sn-2 position of lysophosphatidate | Acyl-CoA or -ACP | 1-Acylglycerol-3-phosphate (lysophosphatidate) | HxxxxD motif (like GPATs) |
| Lpx acyltransferases | LpxA and LpxD from E. coli | First two acylation steps in lipid A biosynthesis | O- and N-acylation of UDP-N-acetylglucosamine and UDP-3-acylglucosamine | 3-Hydroxyacyl-ACP (C14) | UDP-N-acetylglucosamine and UDP-3-O-(3-hydroxymyristoyl)-glucosamine | Catalytically active His (putatively stabilized by adjacent Asp) |
| LpxL from E. coli (homologs: LpxM, LpxP) | Secondary acylation steps in lipid A biosynthesis | O-Acylation of 3-hydroxy fatty acids attached to lipid A precursor (Kdo2-IVA) | Acyl-ACP (C12) (LpxL, acyl-ACP or -CoA; LpxP, C16:1 acyl-ACP) | Kdo2-IVA (tetra-acylated lipid A intermediate) | HxxxxD/E motif (like GPATs) | |
| Polyketide-associated acyltransferases | PapA5 from M. tuberculosis | Synthesis of polyketide-containing complex lipids (e.g., PGL or PDIM) | O-Acylations of phthiocerol with two mycocerosate residues | Unknown donor for mycocerosyl residues; in vitro, long-chain acyl-CoAs (preferred, C16) | (Phenol)phthiocerol, glycosylphenolphthiocerol, linear alcohols (C8–C10; preferred, C8) | (H)HxxxD(G)x13-14Y motif with catalytically active His |
| PapA1 and PapA2 from M. tuberculosis | Synthesis of sulfolipid 1 (SL-1) | O-Acylation of trehalose-2-sulfate | Unknown donor for hydroxyphthioceranoyl residue, C16 acyl-CoA | Trehalose-2-sulfate and trehalose-2-sulfate-2′-palmitate | HxxxD(G)x13-14Y motif | |
| PapA3 from M. tuberculosis | Synthesis of polyketide-containing polyacyltrehalose (PAT) | Successive (?) O-acylations of a trehalose core | Unknown donor for mycolipenoyl residue, C16 acyl-CoA | (Acylated) trehalose | HxxxDx14Y motif | |
| PapA4 from M. marinum | Synthesis of polyketide-containing lipooligosaccharides (LOS) | Successive (?) O-acylations of the trehalose section of LOS | Unknown donor for 2,4-dimethylhexadecanoate and 2,4-dimethyl-2-pentadecenoate residues | (Acylated) trehalose | HxxxDx14Y motif | |
| Rif-Orf20 from A. mediterranei | Rifamycin B biosynthesis | O-Acetylation of a rifamycin B intermediate | Acetyl-CoA (propionyl-CoA) | Rifamycin intermediate | HxxxDx14Y motif | |
| Chloramphenicol acetyltransferase | Type III CAT from E. coli | Inactivation of chloramphenicol | O-Acetylation of chloramphenicol | Acetyl-CoA | Chloramphenicol | HHxxxDG motif catalytically active His |
| RtxC acyltransferases | HlyA from E. coli | Synthesis of (proteinaceous) leukotoxins | N-Acylation of lysine residues of the protoxin | Acyl-ACPs (C12-C18, C16:1, C18:1; preferred, C14) | ε-Amino groups of lysine | Catalytically active His and crucial Ser residue (covalent acyl-HlyC heterocomplex) |
| Lipase | ? | Hydrolysis of acylglycerols | ? | ? | ? | Catalytic triad composed of histidine, serine (in lipase box), and aspartate |
| PHA synthase | ? | Polymerization of 3-hydroxyalkanoic acids to PHA | ? | ? | ? | Catalytic triad composed of histidine, cysteine (in modified lipase box), and aspartate |
| PhaG transacylase | PhaG from P. putida | Metabolic link between de novo fatty acid synthesis and PHAMCL synthesis | (Reversible) transfer of 3-hydroxyacyl-chain from ACP to CoA | 3-Hydroxyacyl-ACP (or -CoA); preferred, 3-hydroxy-C10 | CoA (or ACP) | HxxxxD/A motif, but different mechanism via catalytic triad (composed of Ser, His, and Asp residues) |
| RhlA | RhlA from P. aeruginosa | Metabolic link between de novo fatty acid synthesis and rhamnolipid synthesis (synthesis of HAA) | O-Acylation of the 3-hydroxy group of 3-hydroxyacyl-ACP | 3-Hydroxyacyl-ACPs (preferred, 3-hydroxy-C10) | (3-Hydroxy group of a) 3-hydroxyacyl-residue | Potentially similar mechanism as for PhaG with a catalytic triad |
a
The given catalyzed reactions and (preferred) acyl donors or acceptors refer to the respective model enzyme of each type.