CRYSTAL STRUCTURE OF YEAST NAD-SPECIFIC ISOCITRATE DEHYDROGENASE

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 线粒体NAD特异性异柠檬酸脱氢酶催化的异柠檬酸氧化脱羧为α-酮戊二酸是三羧酸（TCA）循环中的限速步骤。 酵母酶（IDH）对异柠檬酸的亲和力受别构调节，AMP为正，ATP和NADH为负。 已经提出这种变构控制有助于通过氧化途径和糖酵解反向调节能量产生速率。 因此，在能量充足的条件下，即当[ATP]/[AMP]和[NADH]/[NAD]的相对细胞比率高时，通过TCA循环的通量将在IDH水平下减弱，糖酵解速率将增加，并且三羧酸（柠檬酸盐和异柠檬酸盐）将被转移到生物合成途径中。酵母IDH是由四个IDH 1和四个IDH 2亚基组成的八聚体。 IDH1（M.W. = 38，001）和IDH 2（M.W. = 37，755）共有42%的序列同一性。 靶向诱变研究的结果表明，IDH 2亚基含有催化异柠檬酸/Mg 2+和NAD结合位点，而IDH 1亚基中的同源位点在异柠檬酸的合作结合和别构激活剂AMP的结合中起作用。 因此，IDH的寡聚体结构的理解将阐明同源催化和调节配体结合位点之间的关系。 我们已经生产出IDH晶体，其在理学FR-D旋转阳极X射线源上的作用为3.2 μ m。 我们预计，IDH在晶体结构中的低聚排列的测定将揭示这种复杂酶的变构控制模式。此外，结构提供的信息将指导未来的实验研究IDH酶学。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The oxidative decarboxylation of isocitrate to alpha-ketoglutarate catalyzed by mitochondrial NAD-specific isocitrate dehydrogenases is a rate limiting step in the tricarboxylic acid (TCA) cycle. The affinity of the yeast enzyme (IDH) for isocitrate is allosterically regulated, positively by AMP and negatively by ATP and NADH. This allosteric control has been proposed to contribute to inverse regulation of rates of energy production by oxidative pathways and by glycolysis. Thus, under conditions of energy sufficiency, i.e. when relative cellular ratios of [ATP]/[AMP] and of [NADH]/[NAD] are high, flux through the TCA cycle would be attenuated at the level of IDH, rates of glycolysis would increase, and the tricarboxylic acids, citrate and isocitrate, would be diverted into biosynthetic pathways. Yeast IDH is an octamer composed of four IDH1 and four IDH2 subunits. IDH1 (M.W. = 38,001) and IDH2 (M.W. = 37,755) share 42% sequence identity. Results of targeted mutagenesis studies suggest that the IDH2 subunit contains catalytic isocitrate/Mg2+ and NAD binding sites, whereas homologous sites in the IDH1 subunit function in cooperative binding of isocitrate and in binding of the allosteric activator AMP. An understanding of the oligomeric structure of IDH would thus illuminate relationships between homologous catalytic and regulatory ligand binding sites. We have produced crystals of IDH that diffract to 3.2¿¿¿& on a Rigaku FR-D rotating anode X-ray source. We anticipate that the determination of the oligomeric arrangement of IDH in the crystal structure will reveal the mode of allosteric control of this complex enzyme. Additionally, the information provided by the structure will direct future experiments investigating IDH enzymology.