Jormakka Mika, Richardson David, Byrne Bernadette, Iwata So
Division of Biomedical Sciences, Imperial College London, SW7 2AZ, UK.
Structure. 2004 Jan;12(1):95-104. doi: 10.1016/j.str.2003.11.020.
The structure of the catalytic and electron-transfer subunits (NarGH) of the integral membrane protein, respiratory nitrate reductase (Nar) has been determined to 2.0 A resolution revealing the molecular architecture of this Mo-bisMGD (molybdopterin-guanine-dinucleotide) containing enzyme which includes a previously undetected FeS cluster. Nar, together with the related enzyme formate dehydrogenase (Fdh-N), is a key enzyme in the generation of proton motive force across the membrane in Escherichia coli nitrate respiration. A comparative study revealed that Nar and Fdh-N employ different approaches for acquiring substrate, reflecting different catalytic mechanisms. Nar uses a very narrow and nonpolar substrate-conducting cavity with a nonspecific substrate binding site, whereas Fdh-N accommodates a wider, positively charged substrate-conducting cavity with a more specific substrate binding site. The Nar structure also demonstrates the first example of an Asp side chain acting as a Mo ligand providing a structural basis for the classification of Mo-bisMGD enzymes.
膜整合蛋白呼吸硝酸盐还原酶（Nar）的催化和电子传递亚基（NarGH）的结构已确定至2.0埃分辨率，揭示了这种含钼双鸟苷二磷酸（Mo-bisMGD）酶的分子结构，其中包括一个先前未检测到的铁硫簇。Nar与相关酶甲酸脱氢酶（Fdh-N）一起，是大肠杆菌硝酸盐呼吸过程中跨膜产生质子动力的关键酶。一项比较研究表明，Nar和Fdh-N采用不同的底物获取方式，反映了不同的催化机制。Nar使用一个非常狭窄且非极性的底物传导腔，带有一个非特异性底物结合位点，而Fdh-N容纳一个更宽、带正电荷的底物传导腔，带有一个更特异性的底物结合位点。Nar的结构还展示了天冬氨酸侧链作为钼配体的首个实例，为Mo-bisMGD酶的分类提供了结构基础。
