Biochemical characterization of rice trehalose-6-phosphate phosphatases supports distinctive functions of these plant enzymes
Biochemical characterization of rice trehalose-6-phosphate phosphatases supports distinctive functions of these plant enzymes
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DOI：
10.1111/j.1742-4658.2007.05658.x
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发表时间：
2007-03-01
期刊：
影响因子：
5.4
通讯作者：
Imai, Ryozo
中科院分区：
文献类型：
--
作者：
Shima, Shuhei;Matsui, Hirokazu;Imai, Ryozo
大量海藻糖在细菌、真菌和无脊椎动物中积累，在那里它作为储存碳水化合物或作为抵抗环境胁迫的保护剂。在高等植物中，检测到海藻糖的水平相当低;因此，已提出该分子的调节或信号传导功能。在许多生物中，海藻糖-6-磷酸磷酸酶是控制海藻糖生物合成最后一步的酶。OsTPP 1和OsTPP 2是水稻营养组织中表达的两个主要海藻糖-6-磷酸酶基因。与我们先前OsTPP 1研究获得的结果类似，酵母海藻糖-6-磷酸磷酸磷酸酶突变体的互补分析和重组蛋白的活性测定表明OsTPP 2编码功能性海藻糖-6-磷酸磷酸磷酸酶。OsTPP 2的表达在低温和其他非生物胁迫下被瞬时诱导。重组OsTPP 1和OsTPP 2的酶特性显示，与来自微生物的海藻糖-6-磷酸酶相比，对海藻糖-6-磷酸具有严格的底物特异性，并且对海藻糖-6-磷酸的Km值低约10倍。OsTPP 1和OsTPP 2也与微生物酶形成鲜明对比，因为它们通常不稳定，当在50 ℃下热处理4 min时几乎完全失去活性。水稻海藻糖-6-磷酸磷酸酶的这些特征与非常低的细胞底物浓度和严格调控的基因表达一致。这些数据也支持海藻糖生物合成响应环境胁迫的植物特异性功能。
Substantial levels of trehalose accumulate in bacteria, fungi, and invertebrates, where it serves as a storage carbohydrate or as a protectant against environmental stresses. In higher plants, trehalose is detected at fairly low levels; therefore, a regulatory or signaling function has been proposed for this molecule. In many organisms, trehalose-6-phosphate phosphatase is the enzyme governing the final step of trehalose biosynthesis. Here we report that OsTPP1 and OsTPP2 are the two major trehalose-6-phosphate phosphatase genes expressed in vegetative tissues of rice. Similar to results obtained from our previous OsTPP1 study, complementation analysis of a yeast trehalose-6-phosphate phosphatase mutant and activity measurement of the recombinant protein demonstrated that OsTPP2 encodes a functional trehalose-6-phosphate phosphatase enzyme. OsTPP2 expression is transiently induced in response to chilling and other abiotic stresses. Enzymatic characterization of recombinant OsTPP1 and OsTPP2 revealed stringent substrate specificity for trehalose 6-phosphate and about 10 times lower K-m values for trehalose 6-phosphate as compared with trehalose-6-phosphate phosphatase enzymes from microorganisms. OsTPP1 and OsTPP2 also clearly contrasted with microbial enzymes, in that they are generally unstable, almost completely losing activity when subjected to heat treatment at 50 degrees C for 4 min. These characteristics of rice trehalose-6-phosphate phosphatase enzymes are consistent with very low cellular substrate concentration and tightly regulated gene expression. These data also support a plant-specific function of trehalose biosynthesis in response to environmental stresses.