Nwaka S, Holzer H
Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany.
Prog Nucleic Acid Res Mol Biol. 1998;58:197-237. doi: 10.1016/s0079-6603(08)60037-9.
The present state of knowledge of the role of trehalose and trehalose hydrolysis catalyzed by trehalase (EC 3.2.1.28) in the yeast Saccharomyces cerevisiae is reviewed. Trehalose is believed to function as a storage carbohydrate because its concentration is high during nutrient limitations and in resting cells. It is also believed to function as a stress metabolite because its concentration increases during certain adverse environmental conditions, such as heat and toxic chemicals. The exact way trehalose may perform the stress function is not understood, and conditions exist under which trehalose accumulation and tolerance to certain stress situations cannot be correlated. Three trehalases have been described in S. cerevisiae: 1) the cytosolic neutral trehalase encoded by the NTH1 gene, and regulated by cAMP-dependent phosphorylation process, nutrients, and temperature; 2) the vacuolar acid trehalase encoded by the ATH1 gene, and regulated by nutrients; and 3) a putative trehalase Nth1p encoded by the NTH2 gene (homolog of the NTH1 gene) and regulated by nutrients and temperature. The neutral trehalase is responsible for intracellular hydrolysis of trehalose, in contrast to the acid trehalase, which is responsible for utilization of extracellular trehalose. The role of the putative trehalase Nth2p in trehalose metabolism is not known. The NTH1 and NTH2 genes are required for recovery of cells after heat shock at 50 degrees C, consistent with their heat inducibility and sequence similarity. Other stressors, such as toxic chemicals, also induce the expression of these genes. We therefore propose that the NTH1 and NTH2 genes have stress-related function and the gene products may be called stress proteins. Whether the stress function of the trehalase genes is linked to trehalose is not clear, and possible mechanisms of stress protective function of the trehalases are discussed.
本文综述了海藻糖及由海藻糖酶（EC 3.2.1.28）催化的海藻糖水解在酿酒酵母中的作用的现有知识。海藻糖被认为作为一种储存碳水化合物发挥作用，因为其在营养限制期间和静息细胞中的浓度较高。它也被认为作为一种应激代谢物发挥作用，因为在某些不利环境条件下，如热和有毒化学物质作用时，其浓度会增加。海藻糖发挥应激功能的确切方式尚不清楚，并且存在海藻糖积累与对某些应激情况的耐受性不相关的情况。在酿酒酵母中已描述了三种海藻糖酶：1）由NTH1基因编码的胞质中性海藻糖酶，受cAMP依赖性磷酸化过程、营养物质和温度调节；2）由ATH1基因编码的液泡酸性海藻糖酶，受营养物质调节；3）由NTH2基因（NTH1基因的同源物）编码的假定海藻糖酶Nth1p，受营养物质和温度调节。与负责利用细胞外海藻糖的酸性海藻糖酶相反，中性海藻糖酶负责细胞内海藻糖的水解。假定的海藻糖酶Nth2p在海藻糖代谢中的作用尚不清楚。NTH1和NTH2基因是细胞在50摄氏度热休克后恢复所必需的，这与其热诱导性和序列相似性一致。其他应激源，如有毒化学物质，也诱导这些基因的表达。因此，我们提出NTH1和NTH2基因具有与应激相关的功能，其基因产物可被称为应激蛋白。海藻糖酶基因的应激功能是否与海藻糖相关尚不清楚，并讨论了海藻糖酶应激保护功能的可能机制。
