Jez J M, Bennett M J, Schlegel B P, Lewis M, Penning T M
Department of Biochemistry & Biophysics, University of Pennsylvania Medical School, 3620Hamilton Walk, Philadelphia, PA 19104, USA.
Biochem J. 1997 Sep 15;326 ( Pt 3)(Pt 3):625-36. doi: 10.1042/bj3260625.
The aldo-keto reductases metabolize a wide range of substrates and are potential drug targets. This protein superfamily includes aldose reductases, aldehyde reductases, hydroxysteroid dehydrogenases and dihydrodiol dehydrogenases. By combining multiple sequence alignments with known three-dimensional structures and the results of site-directed mutagenesis studies, we have developed a structure/function analysis of this superfamily. Our studies suggest that the (alpha/beta)8-barrel fold provides a common scaffold for an NAD(P)(H)-dependent catalytic activity, with substrate specificity determined by variation of loops on the C-terminal side of the barrel. All the aldo-keto reductases are dependent on nicotinamide cofactors for catalysis and retain a similar cofactor binding site, even among proteins with less than 30% amino acid sequence identity. Likewise, the aldo-keto reductase active site is highly conserved. However, our alignments indicate that variation ofa single residue in the active site may alter the reaction mechanism from carbonyl oxidoreduction to carbon-carbon double-bond reduction, as in the 3-oxo-5beta-steroid 4-dehydrogenases (Delta4-3-ketosteroid 5beta-reductases) of the superfamily. Comparison of the proposed substrate binding pocket suggests residues 54 and 118, near the active site, as possible discriminators between sugar and steroid substrates. In addition, sequence alignment and subsequent homology modelling of mouse liver 17beta-hydroxysteroid dehydrogenase and rat ovary 20alpha-hydroxysteroid dehydrogenase indicate that three loops on the C-terminal side of the barrel play potential roles in determining the positional and stereo-specificity of the hydroxysteroid dehydrogenases. Finally, we propose that the aldo-keto reductase superfamily may represent an example of divergent evolution from an ancestral multifunctional oxidoreductase and an example of convergent evolution to the same active-site constellation as the short-chain dehydrogenase/reductase superfamily.
醛糖 - 酮糖还原酶可代谢多种底物，是潜在的药物靶点。这个蛋白质超家族包括醛糖还原酶、醛还原酶、羟基类固醇脱氢酶和二氢二醇脱氢酶。通过将多序列比对与已知的三维结构以及定点诱变研究结果相结合，我们对这个超家族进行了结构/功能分析。我们的研究表明，（α/β）8桶状折叠为依赖NAD(P)(H)的催化活性提供了一个共同的支架，底物特异性由桶状结构C端侧环的变异决定。所有醛糖 - 酮糖还原酶的催化都依赖于烟酰胺辅因子，并且即使在氨基酸序列同一性低于30%的蛋白质之间，也保留着相似的辅因子结合位点。同样，醛糖 - 酮糖还原酶的活性位点高度保守。然而，我们的比对表明，活性位点中单个残基的变异可能会改变反应机制，从羰基氧化还原转变为碳 - 碳双键还原，就像该超家族中的3 - 氧代 - 5β - 类固醇4 - 脱氢酶（Δ4 - 3 - 酮类固醇5β - 还原酶）那样。对所提出的底物结合口袋的比较表明，活性位点附近的54位和118位残基可能是糖和类固醇底物之间的鉴别位点。此外，小鼠肝脏17β - 羟基类固醇脱氢酶和大鼠卵巢20α - 羟基类固醇脱氢酶的序列比对及后续同源建模表明，桶状结构C端侧的三个环在决定羟基类固醇脱氢酶的位置和立体特异性方面可能发挥潜在作用。最后，我们提出醛糖 - 酮糖还原酶超家族可能代表了从祖先多功能氧化还原酶分歧进化的一个例子，以及与短链脱氢酶/还原酶超家族向相同活性位点结构汇聚进化的一个例子。
