No abstract

Acyl carrier protein (ACP) plays an essential role in fatty acid and polyketide biosynthesis, and most of the fatty acid synthases (FASs) and polyketide synthases (PKSs) known to date are characterized with a single ACP for each cycle of chain elongation. Polyunsaturated fatty acid (PUFA) biosynthesis is catalyzed by the PUFA synthase, and all PUFA synthases known to date contain tandem ACPs (ranging from 5 to 9). Using the Pfa PUFA synthase from Shewanella japonica as a model system, we report here that these tandem ACPs are functionally equivalent regardless of their physical location within the PUFA synthase subunit, but the total number of ACPs controls the overall PUFA titer. These findings set the stage to interrogate other domains and subunits of PUFA synthase for their roles in controlling the final PUFA products and could potentially be exploited to improve PUFA production.

Dietary omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), docosahexaenoic acid (DHA, C22:6) and eicosapentaenoic acid (EPA, C20:5) are usually derived from marine fish. Although production of both EPA and DHA has been engineered into land plants, including Arabidopsis, Camelina sativa and Brassica juncea, neither has been produced in commercially relevant amounts in a widely grown crop. We report expression of a microalgal polyketide synthase-like PUFA synthase system, comprising three multidomain polypeptides and an accessory enzyme, in canola (Brassica napus) seeds. This transgenic enzyme system is expressed in the cytoplasm, and synthesizes DHA and EPA de novo from malonyl-CoA without substantially altering plastidial fatty acid production. Furthermore, there is no significant impact of DHA and EPA production on seed yield in either the greenhouse or the field. Canola oil processed from field-grown grain contains 3.7% DHA and 0.7% EPA, and can provide more than 600 mg of omega-3 LC-PUFAs in a 14 g serving.

No abstract

4؆-Oxo-avermectin is a key intermediate in the manufacture of the agriculturally important insecticide emamectin benzoate from the natural product avermectin. Seventeen biocatalytically active Streptomyces strains with the ability to oxidize avermectin to 4؆-oxo-avermectin in a regioselective manner have been discovered in a screen of 3,334 microorganisms. The enzymes responsible for this oxidation reaction in these biocatalytically active strains were found to be cytochrome P450 monooxygenases (CYPs) and were termed Ema1 to Ema17. The genes for Ema1 to Ema17 have been cloned, sequenced, and compared to reveal a new subfamily of CYPs. Ema1 to Ema16 have been overexpressed in Escherichia coli and purified as His-tagged recombinant proteins, and their basic enzyme kinetic parameters have been determined.