Schwarz Benjamin H, Driver Joseph, Peacock Riley B, Dembinski Holly E, Corson Melissa H, Gordon Samuel S, Watson Jeffrey M
Department of Chemistry and Biochemistry, Gonzaga University, Spokane, WA, USA, 99258.
Department of Chemistry and Biochemistry, Gonzaga University, Spokane, WA, USA, 99258.
Biochim Biophys Acta. 2014 Feb;1844(2):457-64. doi: 10.1016/j.bbapap.2013.11.015. Epub 2013 Dec 3.
3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is a key enzyme in endogenous cholesterol biosynthesis in mammals and isoprenoid biosynthesis via the mevalonate pathway in other eukaryotes, archaea and some eubacteria. In most organisms that express this enzyme, it catalyzes the NAD(P)H-dependent reduction of HMG-CoA to mevalonate. We have cloned and characterized the 6x-His-tagged HMGR from the opportunistic lung pathogen Burkholderia cenocepacia. Kinetic characterization shows that the enzyme prefers NAD(H) over NADP(H) as a cofactor, suggesting an oxidative physiological role for the enzyme. This hypothesis is supported by the fact that the Burkholderia cenocepacia genome lacks the genes for the downstream enzymes of the mevalonate pathway. The enzyme exhibits positive cooperativity toward the substrates of the reductive reaction, but the oxidative reaction exhibits unusual double-saturation kinetics, distinctive among characterized HMG-CoA reductases. The unusual kinetics may arise from the presence of multiple active oligomeric states, each with different Vmax values.
3-羟基-3-甲基戊二酰辅酶A还原酶（HMGR）是哺乳动物内源性胆固醇生物合成以及其他真核生物、古细菌和一些真细菌中通过甲羟戊酸途径进行类异戊二烯生物合成的关键酶。在大多数表达这种酶的生物体中，它催化NAD(P)H依赖的HMG-CoA还原为甲羟戊酸。我们已经从机会性肺部病原体洋葱伯克霍尔德菌中克隆并鉴定了带有6x-组氨酸标签的HMGR。动力学特征表明，该酶更喜欢NAD(H)而非NADP(H)作为辅因子，这表明该酶具有氧化生理作用。洋葱伯克霍尔德菌基因组缺乏甲羟戊酸途径下游酶的基因这一事实支持了这一假设。该酶对还原反应的底物表现出正协同性，但氧化反应表现出不寻常的双饱和动力学，这在已鉴定的HMG-CoA还原酶中是独特的。这种不寻常的动力学可能源于存在多种具有不同Vmax值的活性寡聚状态。
