MedicalResearch.com Interview with: Professor Andrew W. Munro FRSC FSB Professor of Molecular Enzymology Manchester Institute of Biotechnology Faculty of Life Sciences University of Manchester Manchester UK MedicalResearch: What is the background for this study? What are the main findings? Dr. Munro: Statins are blockbuster drugs that inhibit the key enzyme in cholesterol synthesis: 3-beta-hydroxymethylglutaryl CoA reductase (HMG-CoA reductase), which catalyzes the rate-limiting step in the biosynthesis of cholesterol. As a consequence, statin drugs reduce levels of low-density lipoprotein (LDL-) cholesterol, are effective against hypercholesterolemia and reduce the risk of atherosclerosis and heart attack. One of the major statin drugs is pravastatin, which is derived from a fungal natural product called compactin. The process of conversion of compactin into pravastatin involves the use of an oxygen-inserting enzyme called a cytochrome P450 (or P450), which catalyzes the hydroxylation of compactin to form pravastatin. In order to produce a more cost-efficient and streamlined route to pravastatin production, our teams from the University of Manchester (UK) and DSM (Delft, The Netherlands) developed a single-step process for pravastatin production. This process involved harnessing the productive efficiency of an industrial strain of the beta-lactam (penicillin-type) antibiotic producing fungus Penicillium chrysogenum. The beta-lactam antibiotic genes were deleted from this organism, and replaced by those encoding for compactin biosynthesis (transferred from a different Penicillium species). This led to high level production of compactin, but also to substantial formation of a partially degraded (deacylated) form. To get around this problem and in order to further improve compactin production, the enzyme responsible for the deacylation (an esterase) was identified and the gene encoding this activity was deleted from the production strain. The final stages of development of the novel, one-step pravastatin production process involved the identification of a suitable P450 enzyme that could catalyze the required hydroxylation of compactin. A bacterial P450 was identified that catalyzed hydroxylation at the correct position on the compactin molecule. However, the stereoselectivity of the reaction was in favour of the incorrect isomer – forming predominantly epi-pravastatin over the desired pravastatin. This was addressed by mutagenesis of the P450 – ultimately leading to a variant (named P450Prava) that hydroxylated compactin with the required stereoselectivity to make pravastatin in large amounts. Determination of the structure of P450Prava in both the substrate-free and compactin-bound forms revealed the conformational changes that underpinned the conversion of the P450 enzyme to a pravastatin synthase. The expression of P450Prava in a compactin-producing strain of P. chrysogenum enabled pravastatin production at over 6 g/L in a fed-batch fermentation process, facilitating an efficient, single-step route to high yield generation of pravastatin. (more…)