Rice D W, Schulz G E, Guest J R
J Mol Biol. 1984 Apr 15;174(3):483-96. doi: 10.1016/0022-2836(84)90332-2.
The elucidation of the primary structure of the Escherichia coli lipoamide dehydrogenase (EC 1.8.1.4) by sequencing the corresponding structural gene (lpd) has enabled a detailed structural comparison between lipoamide dehydrogenase and the related disulphide oxido-reductase, human erythrocyte glutathione reductase (EC 1.6.4.2). Some 28% of the amino acid residues were found to be identical and a striking degree of homology was apparent throughout the polypeptide chains. It was concluded that the two enzymes possess very similar three-dimensional structures with particularly strong conservation of residues around the FAD and NAD(P) binding sites and at the redox centres of the molecules. Significant amino acid substitutions occur in the substrate binding pocket and these include an extra 18 amino acid residues at the C terminus of lipoamide dehydrogenase. Under physiological conditions, lipoamide dehydrogenase and glutathione reductase act in opposite directions, passing reducing equivalents to NAD+ or from NADPH (respectively), and two key substitutions near the redox centre could be associated with this difference in function. This study represents the first direct structural comparison between two related enzymes that are NADP+-linked (glutathione reductase) and NAD+-linked (lipoamide dehydrogenase). The differential recognition of these two cofactors could be explained in terms of amino acid substitutions. A divergent evolutionary relationship between the two enzymes including their NAD and NADP binding domains is fully supported by this analysis.
通过对大肠杆菌硫辛酰胺脱氢酶（EC 1.8.1.4）相应的结构基因（lpd）进行测序，阐明了其一级结构，这使得能够对硫辛酰胺脱氢酶与相关的二硫氧化还原酶——人红细胞谷胱甘肽还原酶（EC 1.6.4.2）进行详细的结构比较。发现约28%的氨基酸残基是相同的，并且在整个多肽链中都有明显的同源性。得出的结论是，这两种酶具有非常相似的三维结构，在FAD和NAD(P)结合位点周围以及分子的氧化还原中心，残基的保守性特别强。在底物结合口袋中发生了显著的氨基酸取代，其中包括硫辛酰胺脱氢酶C末端额外的18个氨基酸残基。在生理条件下，硫辛酰胺脱氢酶和谷胱甘肽还原酶的作用方向相反，分别将还原当量传递给NAD+或从NADPH传递，氧化还原中心附近的两个关键取代可能与这种功能差异有关。这项研究是对两种相关酶——NADP+连接的（谷胱甘肽还原酶）和NAD+连接的（硫辛酰胺脱氢酶）——的首次直接结构比较。这两种辅因子的差异识别可以用氨基酸取代来解释。该分析充分支持了这两种酶之间包括它们的NAD和NADP结合结构域的不同进化关系。
