Trabelsi Nadia, Petit Pierre, Manigand Claude, Langlois d'Estaintot Béatrice, Granier Thierry, Chaudière Jean, Gallois Bernard
CBMN, UMR CNRS 5248, Bâtiment B8, Avenue des Facultés, Université Bordeaux 1, 33405 Talence CEDEX, France.
Acta Crystallogr D Biol Crystallogr. 2008 Aug;D64(Pt 8):883-91. doi: 10.1107/S0907444908017769. Epub 2008 Jul 17.
Dihydroflavonol 4-reductase (DFR) is a key enzyme of the flavonoid biosynthesis pathway which catalyses the NADPH-dependent reduction of 2R,3R-trans-dihydroflavonols to leucoanthocyanidins. The latter are the precursors of anthocyans and condensed tannins, two major classes of phenolic compounds that strongly influence the organoleptic properties of wine. DFR has been investigated in many plant species, but little was known about its structural properties until the three-dimensional structure of the Vitis vinifera enzyme complexed with NADP(+) and its natural substrate dihydroquercetin (DHQ) was described. In the course of the study of substrate specificity, crystals of DFR-NADP(+)-flavonol (myricetin and quercetin) complexes were obtained. Their structures exhibit major changes with respect to that of the abortive DFR-NADP(+)-DHQ complex. Two flavonol molecules bind to the catalytic site in a stacking arrangement and alter its geometry, which becomes incompatible with enzymatic activity. The X-ray structures of both DFR-NADP(+)-myricetin and DFR-NADP(+)-quercetin are reported together with preliminary spectroscopic data. The results suggest that flavonols could be inhibitors of the activity of DFR towards dihydroflavonols.
二氢黄酮醇4-还原酶（DFR）是类黄酮生物合成途径中的一种关键酶，它催化2R,3R-反式二氢黄酮醇依赖NADPH还原为无色花青素。无色花青素是花色苷和缩合单宁的前体，花色苷和缩合单宁是两类主要的酚类化合物，对葡萄酒的感官特性有很大影响。许多植物物种都对DFR进行了研究，但在葡萄DFR与NADP(+)及其天然底物二氢槲皮素（DHQ）形成的酶复合物的三维结构被描述之前，人们对其结构特性了解甚少。在底物特异性研究过程中，获得了DFR-NADP(+)-黄酮醇（杨梅素和槲皮素）复合物的晶体。它们的结构与流产型DFR-NADP(+)-DHQ复合物的结构相比有重大变化。两个黄酮醇分子以堆积排列的方式结合到催化位点并改变其几何形状，这使其与酶活性不相容。同时报道了DFR-NADP(+)-杨梅素和DFR-NADP(+)-槲皮素的X射线结构以及初步的光谱数据。结果表明，黄酮醇可能是DFR对二氢黄酮醇活性的抑制剂。
