Control of β‐Branching in Kalimantacin Biosynthesis: Application of 13C NMR to Polyketide Programming

The presence of β‐branches in the structure of polyketides that possess potent biological activity underpins the widespread importance of this structural feature. Kalimantacin is a polyketide antibiotic with selective activity against staphylococci, and its biosynthesis involves the unprecedented incorporation of three different and sequential β‐branching modifications. We use purified single and multi‐domain enzyme components of the kalimantacin biosynthetic machinery to address in vitro how the pattern of β‐branching in kalimantacin is controlled. Robust discrimination of enzyme products required the development of a generalisable assay that takes advantage of ¹³C NMR of a single ¹³C label incorporated into key biosynthetic mimics combined with favourable dynamic properties of an acyl carrier protein. We report a previously unassigned modular enoyl‐CoA hydratase (mECH) domain and the assembly of enzyme constructs and cascades that are able to generate each specific β‐branch.