Yao Yuan, Wu Xiao-Hui, Geng Meng-Ting, Li Rui-Mei, Liu Jiao, Hu Xin-Wen, Guo Jian-Chun
Key Laboratory of Biology and Genetic Resources of Tropical Crops, Ministry of Agriculture, Institute of Tropical Bioscience and Biotechnology, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China.
Agricultural College, Hainan University, Haikou 571104, China.
Molecules. 2014 May 15;19(5):6228-45. doi: 10.3390/molecules19056228.
Vacuolar invertase is one of the key enzymes in sucrose metabolism that irreversibly catalyzes the hydrolysis of sucrose to glucose and fructose in plants. In this research, three vacuolar invertase genes, named MeVINV1-3, and with 653, 660 and 639 amino acids, respectively, were cloned from cassava. The motifs of NDPNG (β-fructosidase motif), RDP and WECVD, which are conserved and essential for catalytic activity in the vacuolar invertase family, were found in MeVINV1 and MeVINV2. Meanwhile, in MeVINV3, instead of NDPNG we found the motif NGPDG, in which the three amino acids GPD are different from those in other vacuolar invertases (DPN) that might result in MeVINV3 being an inactivated protein. The N-terminal leader sequence of MeVINVs contains a signal anchor, which is associated with the sorting of vacuolar invertase to vacuole. The overall predicted 3D structure of the MeVINVs consists of a five bladed β-propeller module at N-terminus domain, and forms a β-sandwich module at the C-terminus domain. The active site of the protein is situated in the β-propeller module. MeVINVs are classified in two subfamilies, α and β groups, in which α group members of MeVINV1 and 2 are highly expressed in reproductive organs and tuber roots (considered as sink organs), while β group members of MeVINV3 are highly expressed in leaves (source organs). All MeVINVs are highly expressed in leaves, while only MeVINV1 and 2 are highly expressed in tubers at cassava tuber maturity stage. Thus, MeVINV1 and 2 play an important role in sucrose unloading and starch accumulation, as well in buffering the pools of sucrose, hexoses and sugar phosphates in leaves, specifically at later stages of plant development.
液泡转化酶是蔗糖代谢中的关键酶之一，它在植物中不可逆地催化蔗糖水解为葡萄糖和果糖。在本研究中，从木薯中克隆了三个液泡转化酶基因，分别命名为MeVINV1 - 3，其氨基酸长度分别为653、660和639个。在MeVINV1和MeVINV2中发现了NDPNG（β - 果糖苷酶基序）、RDP和WECVD基序，这些基序在液泡转化酶家族中对于催化活性是保守且必不可少的。同时，在MeVINV3中，我们发现其基序为NGPDG，而非NDPNG，其中三个氨基酸GPD与其他液泡转化酶中的DPN不同，这可能导致MeVINV3成为一种无活性的蛋白质。MeVINVs的N端前导序列包含一个信号锚，这与液泡转化酶向液泡的分选有关。MeVINVs的整体预测三维结构在N端结构域由一个五叶β - 螺旋桨模块组成，在C端结构域形成一个β - 三明治模块。该蛋白质的活性位点位于β - 螺旋桨模块中。MeVINVs分为α和β两个亚家族，其中MeVINV1和2的α组成员在生殖器官和块根（被视为库器官）中高表达，而MeVINV3的β组成员在叶片（源器官）中高表达。所有MeVINVs在叶片中均高表达，而在木薯块根成熟阶段，只有MeVINV1和2在块根中高表达。因此，MeVINV1和2在蔗糖卸载和淀粉积累中发挥重要作用，同时也在缓冲叶片中蔗糖、己糖和糖磷酸酯库方面发挥重要作用，特别是在植物发育的后期阶段。
