Ahmad Laziana, Rylott Elizabeth L, Bruce Neil C, Edwards Robert, Grogan Gideon
York Structural Biology Laboratory Department of Chemistry University of York UK; Department of Biology Centre for Novel Agricultural Products University of York UK.
Department of Biology Centre for Novel Agricultural Products University of York UK.
FEBS Open Bio. 2016 Dec 22;7(2):122-132. doi: 10.1002/2211-5463.12168. eCollection 2017 Feb.
Glutathione transferases (GSTs) are involved in many processes in plant biochemistry, with their best characterised role being the detoxification of xenobiotics through their conjugation with glutathione. GSTs have also been implicated in noncatalytic roles, including the binding and transport of small heterocyclic ligands such as indole hormones, phytoalexins and flavonoids. Although evidence for ligand binding and transport has been obtained using gene deletions and ligand binding studies on purified GSTs, there has been no structural evidence for the binding of relevant ligands in noncatalytic sites. Here we provide evidence of noncatalytic ligand-binding sites in the phi class GST from the model plant , GSTF2, revealed by X-ray crystallography. Complexes of the GSTF2 dimer were obtained with indole-3-aldehyde, camalexin, the flavonoid quercetrin and its non-rhamnosylated analogue quercetin, at resolutions of 2.00, 2.77, 2.25 and 2.38 Å respectively. Two symmetry-equivalent-binding sites () were identified at the periphery of the dimer, and one more () at the dimer interface. In the complexes, indole-3-aldehyde and quercetrin were found at both and sites, but camalexin was found only at the sites and quercetin only at the site. Ligand binding at each site appeared to be largely determined through hydrophobic interactions. The crystallographic studies support previous conclusions made on ligand binding in noncatalytic sites by GSTF2 based on isothermal calorimetry experiments (Dixon . (2011) , 63-70) and suggest a mode of ligand binding in GSTs commensurate with a possible role in ligand transport.
谷胱甘肽转移酶（GSTs）参与植物生物化学的许多过程，其最显著的作用是通过与谷胱甘肽结合来解毒异源生物。GSTs也被认为具有非催化作用，包括结合和运输小分子杂环配体，如吲哚激素、植保素和类黄酮。尽管通过基因缺失和对纯化的GSTs进行配体结合研究获得了配体结合和运输的证据，但尚未有关于相关配体在非催化位点结合的结构证据。在这里，我们提供了通过X射线晶体学揭示的模式植物拟南芥phi类GST（GSTF2）中非催化配体结合位点的证据。分别以2.00、2.77、2.25和2.38 Å的分辨率获得了GSTF2二聚体与吲哚 - 3 - 醛、camalexin、类黄酮槲皮苷及其非鼠李糖基化类似物槲皮素的复合物。在二聚体的外围鉴定出两个对称等效的结合位点（），在二聚体界面处还鉴定出一个（）。在复合物中，吲哚 - 3 - 醛和槲皮苷在和位点均有发现，但camalexin仅在位点发现，槲皮素仅在位点发现。每个位点的配体结合似乎主要由疏水相互作用决定。晶体学研究支持了先前基于等温滴定量热实验（Dixon. (2011), 63 - 70）对GSTF2在非催化位点配体结合得出的结论，并提出了GSTs中配体结合的模式，这与配体运输中的可能作用相符。
