Functional Characterization of 3‐Aminobenzoic Acid Adenylation Enzyme PctU and UDP‐N‐Acetyl‐d‐Glucosamine: 3‐Aminobenzoyl‐ACP Glycosyltransferase PctL in Pactamycin Biosynthesis

Pactamycin is an antibiotic produced by Streptomyces pactum with antitumor and antimalarial properties. Pactamycin has a unique aminocyclitol core that is decorated with 3‐aminoacetophenone, 6‐methylsaliciate, and an N,N‐dimethylcarbamoyl group. Herein, we show that the adenylation enzyme PctU activates 3‐aminobenzoic acid (3ABA) with adenosine triphosphate and ligates it to the holo form of the discrete acyl carrier protein PctK to yield 3ABA‐PctK. Then, 3ABA‐PctK is N‐glycosylated with uridine diphosphate‐N‐acetyl‐d‐glucosamine (UDP‐GlcNAc) by the glycosyltransferase PctL to yield GlcNAc‐3ABA‐PctK. Because 3ABA is known to be a precursor of the 3‐aminoacetophenone moiety, PctU appears to be a gatekeeper that selects the appropriate 3‐aminobenzoate starter unit. Overall, we propose that acyl carrier protein‐bound glycosylated 3ABA derivatives are biosynthetic intermediates of pactamycin biosynthesis. Start as you mean to go on: The adenylation enzyme PctU activates 3‐aminobenzoic acid (3ABA) and ligates it with a discrete acyl carrier protein to yield 3ABA‐PctK in early‐stage pactamycin biosynthesis. Next, the glycosyltransferase PctL catalyzes the N‐glycosylation of 3ABA‐PctK with uridine diphosphate‐N‐acetyl‐d‐glucosamine (GlcNAc) to yield GlcNAc‐3ABA‐PctK as the initial ACP‐bound biosynthetic intermediate.