Highly reducing iterative polyketide synthases are large, multifunctional enzymes that make important metabolites in fungi, such as lovastatin, a cholesterol-lowering drug from Aspergillus terreus. ...We report efficient expression of the lovastatin nonaketide synthase (LovB) from an engineered strain of Saccharomyces cerevisiae, as well as complete reconstitution of its catalytic function in the presence and absence of cofactors (the reduced form of nicotinamide adenine dinucleotide phosphate and S-adenosylmethionine) and its partner enzyme, the enoyl reductase LovC. Our results demonstrate that LovB retains correct intermediates until completion of synthesis of dihydromonacolin L, but off-loads incorrectly processed compounds as pyrones or hydrolytic products. Experiments replacing LovC with analogous MlcG from compactin biosynthesis demonstrate a gate-keeping function for this partner enzyme. This study represents a key step in the understanding of the functions and structures of this family of enzymes.
A convergent, nine‐step (LLS), enantioselective synthesis of α‐cyclopiazonic acid and related natural products is reported. The route features a) an enantioselective aziridination of an imine with a ...chiral sulfur ylide; b) a bioinspired (3+2)‐cycloaddition of the aziridine onto an alkene; and c) installation of the acetyltetramic acid by an unprecedented tandem carbonylative lactamization/N−O cleavage of a bromoisoxazole.
A convergent, nine‐step (longest linear sequence), enantioselective synthesis of α‐cyclopiazonic acid is reported featuring a) an enantioselective aziridination; b) a bioinspired (3+2)‐cycloaddition; and c) an unprecedented tandem carbonylative lactamization/N−O cleavage of a bromoisoxazole to install the acetyltetramic acid.
Diaminopimelate (DAP) epimerase is a key enzyme for the biosynthesis of lysine in plants. Lysine is an essential dietary nutrient for mammals. In both plants and bacteria, DAP epimerase catalyzes the ...interconversion of
ll-DAP and
dl(
meso)-DAP. The absence of a mammalian homolog makes DAP epimerase a promising target for the design of novel herbicides and antibacterials. This enzyme requires no cofactors and it functions through an unusual mechanism involving two cysteine residues acting in concert and alternating as a base (thiolate) and as an acid (thiol). The present study reports the crystal structures of two enzyme–inhibitor complexes of DAP epimerase from
Arabidopsis thaliana with different isomers of the irreversible inhibitor and substrate mimic, 2-(4-amino-4-carboxybutyl)-aziridine-2-carboxylate, at 1.95 and 2.3 Å resolution. These structures provide the first atomic details of a plant amino acid racemase. Structural analysis reveals that ligand binding to a cleft between the two domains of the enzyme is accompanied by domain closure with two strictly conserved cysteine residues, Cys99 and Cys254, optimally positioned to perform acid/base catalysis
via a carbanion stabilization mechanism on the stereogenic α-carbon atom of the amino acid. Stereochemical control in catalysis is achieved by means of a highly symmetric catalytic site that can accommodate both the
l and
d stereogenic centers of DAP at the proximal site, whereas specific interactions at the distal site require only the
l configuration. Structural comparisons of the plant enzyme with its bacterial counterpart from
Haemophilus influenzae reveal significant conservation of amino acid residues around the active site that extends to their three-dimensional structures and catalytic mechanism.
A convergent, nine‐step (LLS), enantioselective synthesis of α‐cyclopiazonic acid and related natural products is reported. The route features a) an enantioselective aziridination of an imine with a ...chiral sulfur ylide; b) a bioinspired (3+2)‐cycloaddition of the aziridine onto an alkene; and c) installation of the acetyltetramic acid by an unprecedented tandem carbonylative lactamization/N−O cleavage of a bromoisoxazole.
Eine konvergente enantioselektive Synthese von α‐Cyclopiazonsäure mit neun Stufen in der längsten linearen Sequenz wird beschrieben. Die Schlüsselschritte sind: a) eine enantioselektive Aziridinierung, b) eine biologisch inspirierte (3+2)‐Cycloaddition und c) eine Tandemreaktion aus carbonylierender Lactamisierung und N‐O‐Spaltung eines Bromisoxazols zur Einführung der Acetyltetramsäure.
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