Zhou Yuanze, Liao Lijing, Liu Xikai, Liu Biao, Chen Xinxin, Guo Yan, Huang Chuanlong, Zhao Yucheng, Zeng Zhixiong
National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan 430070, China.
Jiangsu Key Laboratory of Bioactive Natural Product Research and State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210014, China.
J Adv Res. 2020 Jun 12;24:501-511. doi: 10.1016/j.jare.2020.06.004. eCollection 2020 Jul.
Plant tryptophan decarboxylase (TDC) is a type II Pyridoxal-5'-phosphate-dependent decarboxylase (PLP_DC) that could be used as a target to genetically improve crops. However, lack of accurate structural information on plant TDC hampers the understanding of its decarboxylation mechanisms. In the present study, the crystal structures of TDC (sTDC) in its complexes with pyridoxal-5'-phosphate, tryptamine and serotonin were determined. The structures provide detailed interaction information between TDC and its substrates. The Y359 residue from the loop gate is a proton donor and forms a Lewis acid-base pair with serotonin/tryptamine, which is associated with product release. The H214 residue is responsible for PLP binding and proton transfer, and its proper interaction with Y359 is essential for TDC enzyme activity. The extra hydrogen bonds formed between the 5-hydroxyl group of serotonin and the backbone carboxyl groups of F104 and P105 explain the discrepancy between the catalytic activity of TDC in tryptophan and in 5-hydroxytryptophan. In addition, an evolutionary analysis revealed that type II PLP_DC originated from glutamic acid decarboxylase, potentially as an adaptive evolution of mechanism in organisms in extreme environments. This study is, to our knowledge, the first to present a detailed analysis of the crystal structure of TDC in these complexes. The information regarding the catalytic mechanism described here could facilitate the development of protocols to regulate melatonin levels and thereby contribute to crop improvement efforts to improve food security worldwide.
植物色氨酸脱羧酶（TDC）是一种II型依赖磷酸吡哆醛的脱羧酶（PLP_DC），可作为基因改良作物的靶点。然而，缺乏关于植物TDC的准确结构信息阻碍了对其脱羧机制的理解。在本研究中，测定了TDC（sTDC）与磷酸吡哆醛、色胺和5-羟色胺复合物的晶体结构。这些结构提供了TDC与其底物之间详细的相互作用信息。来自环门的Y359残基是质子供体，与5-羟色胺/色胺形成路易斯酸碱对，这与产物释放有关。H214残基负责PLP结合和质子转移，其与Y359的适当相互作用对TDC酶活性至关重要。5-羟色胺的5-羟基与F104和P105的主链羧基之间形成的额外氢键解释了TDC对色氨酸和5-羟基色氨酸催化活性的差异。此外，进化分析表明，II型PLP_DC起源于谷氨酸脱羧酶，可能是极端环境中生物体机制的适应性进化。据我们所知，本研究首次对这些复合物中TDC的晶体结构进行了详细分析。此处描述的催化机制信息有助于制定调节褪黑素水平的方案，从而为提高全球粮食安全的作物改良工作做出贡献。
