Effects of overproduction of the catalytic domain of 3-hydroxy-3-methylglutaryl coenzyme A reductase on squalene synthesis in Saccharomyces cerevisiae.
The enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMG-R) is the major rate-limiting enzyme of the mevalonate pathway in many organisms, including yeasts. In the yeast Saccharomyces cerevisiae, there are two isoenzymes of HMG-R (Hmg1p and Hmg2p). Both consist of an anchoring transmembrane domain and a catalytic domain. We have removed the known controlling features of HMG-R by overproducing the catalytic domain of Hmg1p. This overproduction leads to an enhancement of squalene production, implying that HMG-R has been deregulated. The enhancement is apparent under semianaerobic and aerobic conditions. Despite the increase in squalene production, the amount of ergosterol produced by the HMG-R-overproducing yeast was not increased. This result suggests the presence of another regulatory step between squalene and ergosterol formation. Squalene levels generated by cells overproducing the catalytic domain of HMG-R were estimated to be up to 10 times those produced by wild-type cells. The enhancement in squalene production coincided with a reduction in growth rate. This reduction may be a direct consequence of the buildup of high concentrations of squalene and presqualene intermediates of the pathway.
Donald
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Department of Cellular Physiology, Babraham Institute, Cambridge, United Kingdom. allen.donald@bbsrc.ac.uk
Hampton
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Fritz
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D000332:Aerobiosis; D000693:Anaerobiosis; D001483:Base Sequence; D001665:Binding Sites; D002384:Catalysis; D004271:DNA, Fungal / Q000235:genetics; D004875:Ergosterol / Q000096:biosynthesis; D005800:Genes, Fungal; D006903:Hydroxymethylglutaryl CoA Reductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015394:Molecular Structure; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D013185:Squalene / Q000378:metabolism*
D004271:DNA, Fungal; D012331:RNA, Fungal; D012333:RNA, Messenger; D013185:Squalene; D006903:Hydroxymethylglutaryl CoA Reductases; D004875:Ergosterol