Fan Chunxin, Zhang Shicui, Liu Zhenhui, Li Lei, Luan Jing, Saren Gaowa
Department of Marine Biology, Ocean University of China, Qingdao 266003, China.
Int J Biochem Cell Biol. 2007;39(2):450-61. doi: 10.1016/j.biocel.2006.09.013. Epub 2006 Oct 12.
Glutathione-S-transferases have been identified in all the living species examined so far, yet little is known to date about them in amphioxus, a model organism for insights into the origin and evolution of vertebrates. We have isolated a cDNA encoding an amphioxus (Branchiostoma belcheri) glutathione-S-transferase with a predicted molecular mass of approximately 26 kDa, from the gut cDNA library. The glutathione-S-transferase had 43.7-51.8% identity to most glutathione-S-transferases identified from aquatic organisms including fish and green alga, but it was much less identical (<27%) to other cytosolic glutathione-S-transferase classes. The phylogenetic analysis revealed that the glutathione-S-transferase was grouped together with most piscine and algal glutathione-S-transferases, separating from other cytosolic glutathione-S-transferase classes. Moreover, the glutathione-S-transferase had an exon-intron organization typical of zebrafish putative GST, red sea bream GSTR1 and plaice GSTA1 genes. The recombinant glutathione-S-transferase has been successfully expressed and purified, which showed a relatively high catalytic activity (3.37+/-0.1 unit/mg) toward 1-chloro-2, 4-dinitrobenzene and a moderate activity toward ethacrynic acid (0.41+/-0.01 unit/mg), although it had no detectable activity toward 1, 2-dichloro-4-nitrobenzene, 4-hydroxynonenal, 4-nitrobenzyl chloride and cumene hydroperoxide. In addition, we have revealed a tissue-specific expression pattern of the glutathione-S-transferase gene in B. belcheri, with the most abundant expression in the hepatic caecum. All these indicate that the amphioxus glutathione-S-transferase belongs to a novel rho-class of glutathione-S-transferases with a tissue-specific expression pattern. The relation between the glutathione-S-transferase expression in amphioxus hepatic caecum and the origin of vertebrate liver is also discussed.
迄今为止，在所有已检测的生物物种中均已鉴定出谷胱甘肽 - S - 转移酶，但对于文昌鱼（一种用于深入了解脊椎动物起源和进化的模式生物）中谷胱甘肽 - S - 转移酶的了解目前还很少。我们从肠道cDNA文库中分离出了一个编码文昌鱼（白氏文昌鱼）谷胱甘肽 - S - 转移酶的cDNA，预测分子量约为26 kDa。该谷胱甘肽 - S - 转移酶与从包括鱼类和绿藻在内的水生生物中鉴定出的大多数谷胱甘肽 - S - 转移酶具有43.7 - 51.8%的同一性，但与其他胞质谷胱甘肽 - S - 转移酶类别相比，其同一性要低得多（<27%）。系统发育分析表明，该谷胱甘肽 - S - 转移酶与大多数鱼类和藻类谷胱甘肽 - S - 转移酶归为一类，与其他胞质谷胱甘肽 - S - 转移酶类别分开。此外，该谷胱甘肽 - S - 转移酶具有斑马鱼推定的GST、真鲷GSTR1和平鲷GSTA1基因典型的外显子 - 内含子结构。重组谷胱甘肽 - S - 转移酶已成功表达并纯化，它对1 - 氯 - 2,4 - 二硝基苯表现出相对较高的催化活性（3.37±0.1单位/毫克），对依他尼酸表现出中等活性（0.41±0.01单位/毫克），尽管它对1,2 - 二氯 - 4 - 硝基苯、4 - 羟基壬烯醛、4 - 硝基苄基氯和氢过氧化异丙苯没有可检测到的活性。此外，我们还揭示了白氏文昌鱼中谷胱甘肽 - S - 转移酶基因的组织特异性表达模式，在肝盲囊中表达最为丰富。所有这些表明，文昌鱼谷胱甘肽 - S - 转移酶属于具有组织特异性表达模式的新型rho类谷胱甘肽 - S - 转移酶。同时还讨论了文昌鱼肝盲囊中谷胱甘肽 - S - 转移酶表达与脊椎动物肝脏起源之间的关系。
