Nonreducing polyketide synthases (NR-PKSs) are unique among PKSs in their domain structure, notably including a starter unit:acyl-carrier protein (ACP) transacylase (SAT) domain that selects an acyl group as the primer for biosynthesis, most commonly acetyl-CoA from central metabolism. This clan of mega-enzymes resembles fatty acid synthases (FASs) by sharing both their central chain elongation steps and their capacity for iterative catalysis. In this mode of synthesis, catalytic domains involved in chain extension exhibit substrate plasticity to accommodate growing chains as small as two carbons to 20 or more.
View Article and Find Full Text PDFLovastatin is an important statin prescribed for the treatment and prevention of cardiovascular diseases. Biosynthesis of lovastatin uses an iterative type I polyketide synthase (PKS). LovC is a trans-acting enoyl reductase (ER) that specifically reduces three out of eight possible polyketide intermediates during lovastatin biosynthesis.
View Article and Find Full Text PDFLovastatin, a cyclic nonaketide from Aspergillus terreus, is a hypercholesterolemic agent and a precursor to simvastatin, a semi-synthetic cholesterol-lowering drug. The biosynthesis of the lovastatin backbone (dihydromonacolin L) and the final 2-methylbutyryl decoration have been fully characterized. However, it remains unclear how two central reactions are catalyzed, namely, introduction of the 4a,5-double bond and hydroxylation at C-8.
View Article and Find Full Text PDFHypothemycin is a macrolide protein kinase inhibitor from the fungus Hypomyces subiculosus. During biosynthesis, its carbon framework is assembled by two iterative polyketide synthases (PKSs), Hpm8 (highly reducing) and Hpm3 (nonreducing). These were heterologously expressed in Saccharomyces cerevisiae BJ5464-NpgA, purified to near homogeneity, and reconstituted in vitro to produce (6'S,10'S)-trans-7',8'-dehydrozearalenol (1) from malonyl-CoA and NADPH.
View Article and Find Full Text PDFHighly 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.
View Article and Find Full Text PDFHistorically, the majority of new drugs have been generated from natural products (secondary metabolites) and from compounds derived from natural products. During the past 15 years, pharmaceutical industry research into natural products has declined, in part because of an emphasis on high-throughput screening of synthetic libraries. Currently there is substantial decline in new drug approvals and impending loss of patent protection for important medicines.
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