Donald K A, Hampton R Y, Fritz I B
Department of Cellular Physiology, Babraham Institute, Cambridge, United Kingdom.
Appl Environ Microbiol. 1997 Sep;63(9):3341-4. doi: 10.1128/aem.63.9.3341-3344.1997.
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.
3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）还原酶（HMG-R）是包括酵母在内的许多生物体中甲羟戊酸途径的主要限速酶。在酿酒酵母中，HMG-R有两种同工酶（Hmg1p和Hmg2p）。两者都由一个锚定跨膜结构域和一个催化结构域组成。我们通过过量表达Hmg1p的催化结构域去除了HMG-R已知的调控特征。这种过量表达导致角鲨烯产量增加，这意味着HMG-R的调控已被解除。这种增加在半厌氧和好氧条件下都很明显。尽管角鲨烯产量增加，但过量表达HMG-R的酵母产生的麦角固醇量并未增加。这一结果表明在角鲨烯和麦角固醇形成之间存在另一个调控步骤。过量表达HMG-R催化结构域的细胞产生的角鲨烯水平估计是野生型细胞产生的角鲨烯水平的10倍。角鲨烯产量的增加与生长速率的降低同时出现。这种降低可能是该途径中高浓度角鲨烯和前角鲨烯中间体积累的直接结果。
