α,β → β,γ double bond migration in corallopyronin A biosynthesis

Abstract

In polyketide biosynthesis the reduction of β-carbonyl groups to an alkene usually results in a α,β double bond. However, in a few antibiotics the rare case of such a carbon–carbon double bond in β,γ position is observed. The in vivo active antibiotic corallopyronin A represents such a molecule, whereby a α,β → β,γ double bond migration takes place during the assembly of the molecule. Here we report the in vitro analysis of the enzyme domain responsible for this double bond isomerization. This “shift domain” was heterologously expressed and assayed with its acyl carrier protein bound substrate. To facilitate this analysis the biosynthetic corallopyronin A intermediate was chemically synthesized as a SNAC-derivative. Enzyme activity was analyzed by NMR and high-resolution MS measurements, the latter enabled by performing the assay in deuterated buffer. Mutated enzyme variants gave first experimental evidence for the essential amino acids involved in double bond migration. These results further support the proposed corallopyronin A biosynthesis.