# Programmed Iteration Controls the Assembly of the Nonanoic Acid Side Chain of the Antibiotic Mupirocin

## TL;DR

Scientists uncovered how a key part of the antibiotic mupirocin is built, using advanced techniques to track chemical steps.

## Contribution

The study reveals the biosynthetic pathway of the 9-hydroxynonanoic acid side chain in mupirocin using NMR and mass spectrometry.

## Key findings

- The 9-hydroxynonanoic acid side chain is assembled from a 3-hydroxypropionate starter unit.
- A novel iterative KS-AT didomain (MmpF) and multiple ACPs are involved in the biosynthesis.
- The findings provide insights for engineering trans-AT biosynthetic pathways.

## Abstract

Mupirocin is a clinically important antibiotic produced by Pseudomonas fluorescens NCIMB 10586 that is assembled by a complex trans‐AT polyketide synthase. The polyketide fragment, monic acid, is esterified by a 9‐hydroxynonanoic acid (9HN) side chain which is essential for biological activity. The ester side chain assembly is initialised from a 3‐hydroxypropionate (3HP) starter unit attached to the acyl carrier protein (ACP) MacpD, but the fate of this species is unknown. Herein we report the application of NMR spectroscopy, mass spectrometry, chemical probes and in vitro assays to establish the remaining steps of 9HN biosynthesis. These investigations reveal a complex interplay between a novel iterative or “stuttering” KS‐AT didomain (MmpF), the multidomain module MmpB and multiple ACPs. This work has important implications for understanding the late‐stage biosynthetic steps of mupirocin and will be important for future engineering of related trans‐AT biosynthetic pathways (e.g. thiomarinol).