The X-ray structure of Brassica napus beta-keto acyl carrier proteinreductase and its implications for substrate binding and catalysis

AbstractBackground: β-Keto acyl carrier protein reductase (BKR) catalyzes the pyridine-nucleotide-dependent reduction of a 3-oxoacyl form of acyl carrier protein (ACP), the first reductive step in de novo fatty acid biosynthesis and a reaction often performed in polyketide biosynthesis. The Brassica napus BKR enzyme is NADPH-dependent and forms part of a dissociable type II fatty acid synthetase (FAS). Significant sequence similarity is observed with enoyl acyl carrier protein reductase (ENR), the other reductase of FAS, and the short-chain alcohol dehydrogenase (SDR) family.Results: The first crystal structure of BKR has been determined at 2.3 Å resolution in a binary complex with an NADP+ cofactor. The structure reveals a homotetramer in which each subunit has a classical dinucleotide-binding fold. A triad of Ser154, Tyr167 and Lys171 residues is found at the active site, characteristic of the SDR family. Overall BKR has a very similar structure to ENR with good superimposition of catalytically important groups. Modelling of the substrate into the active site of BKR indicates the need for conformational changes in the enzyme.Conclusions: A catalytic mechanism can be proposed involving the conserved triad. Helix α6 must shift its position to permit substrate binding to BKR and might act as a flexible lid on the active site. The similarities in fold, mechanism and substrate binding between BKR, which catalyzes a carbon–oxygen double-bond reduction, and ENR, the carbon–carbon double-bond oxidoreductase in FAS, suggest a close evolutionary link during the development of the fatty acid biosynthetic pathway

REGULATION OF PLANT GENE-EXPRESSION BY ANTISENSE RNA

Regulation of gene expression by antisense RNA was first discovered as a naturally-occurring phenomenon in bacteria. Recently natural antisense RNAs have been found in a variety of eukaryotic organisms; their in vivo function is, however, obscure. Deliberate expression of antisense RNA in animal and plant systems has lead to successful down-regulation of specific genes. We will review the current status of antisense gene action in plant systems. The recent discovery that 'sense' genes are able to mimic the action of antisense genes indicates that (anti)sense genes must operate by mechanisms other than RNA-RNA interaction. © 1990