Structural evidence for Arabidopsis glutathione transferase AtGSTF2 functioning as a transporter of small organic ligands.
Structural evidence for Arabidopsis glutathione transferase AtGSTF2 functioning as a transporter of small organic ligands.
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DOI：
10.1002/2211-5463.12168
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发表时间：
2017-02
期刊：
影响因子：
2.6
通讯作者：
Grogan G
中科院分区：
文献类型：
--
作者：
Ahmad L;Rylott EL;Bruce NC;Edwards R;Grogan G
谷胱甘肽转移酶（GST）参与植物生物化学中的许多过程，其最具特征的作用是通过与谷胱甘肽结合来解毒异生物质。GST也参与非催化作用，包括小杂环配体如吲哚激素、植物抗毒素和类黄酮的结合和转运。虽然证据配体结合和运输已获得纯化GST基因缺失和配体结合的研究，一直没有相关的配体在非催化位点的结合的结构证据。在这里，我们提供了来自模式植物拟南芥AtGSTF 2的phi类GST中的非催化配体结合位点的证据，这些证据是通过X射线晶体学揭示的。AtGSTF 2二聚体与吲哚-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分别以2.00、2.77、2.25和2.38 μ m的分辨率获得。在二聚体的外围确定了两个对称等效结合位点（L1），在二聚体界面确定了另一个对称等效结合位点（L2）。在复合物中，吲哚-3-醛和槲皮苷在L1和L2位点都被发现，但camalexin仅在L1位点被发现，槲皮素仅在L2位点被发现。在每个站点的配体结合似乎在很大程度上是通过疏水相互作用确定的。晶体学研究支持先前基于等温量热实验（狄克逊等人（2011）Biochem J 438，63-70）对AtGSTF 2在非催化位点中的配体结合做出的结论，并提出了与配体转运中的可能作用相称的GST中的配体结合模式。
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 Arabidopsis thaliana, AtGSTF2, revealed by X‐ray crystallography. Complexes of the AtGSTF2 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 (L1) were identified at the periphery of the dimer, and one more (L2) at the dimer interface. In the complexes, indole‐3‐aldehyde and quercetrin were found at both L1 and L2 sites, but camalexin was found only at the L1 sites and quercetin only at the L2 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 AtGSTF2 based on isothermal calorimetry experiments (Dixon et al. (2011) Biochem J 438, 63–70) and suggest a mode of ligand binding in GSTs commensurate with a possible role in ligand transport.