Goyal K, Browne J A, Burnell A M, Tunnacliffe A
Institute of Biotechnology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QT, UK.
Biochimie. 2005 Jun;87(6):565-74. doi: 10.1016/j.biochi.2005.01.010. Epub 2005 Feb 12.
Accumulation of the non-reducing disaccharide trehalose is associated with desiccation tolerance during anhydrobiosis in a number of invertebrates, but there is little information on trehalose biosynthetic genes in these organisms. We have identified two trehalose-6-phosphate synthase (tps) genes in the anhydrobiotic nematode Aphelenchus avenae and determined full length cDNA sequences for both; for comparison, full length tps cDNAs from the model nematode, Caenorhabditis elegans, have also been obtained. The A. avenae genes encode very similar proteins containing the catalytic domain characteristic of the GT-20 family of glycosyltransferases and are most similar to tps-2 of C. elegans; no evidence was found for a gene in A. avenae corresponding to Ce-tps-1. Analysis of A. avenae tps cDNAs revealed several features of interest, including alternative trans-splicing of spliced leader sequences in Aav-tps-1, and four different, novel SL1-related trans-spliced leaders, which were different to the canonical SL1 sequence found in all other nematodes studied. The latter observation suggests that A. avenae does not comply with the strict evolutionary conservation of SL1 sequences observed in other species. Unusual features were also noted in predicted nematode TPS proteins, which distinguish them from homologues in other higher eukaryotes (plants and insects) and in micro-organisms. Phylogenetic analysis confirmed their membership of the GT-20 glycosyltransferase family, but indicated an accelerated rate of molecular evolution. Furthermore, nematode TPS proteins possess N- and C-terminal domains, which are unrelated to those of other eukaryotes: nematode C-terminal domains, for example, do not contain trehalose-6-phosphate phosphatase-like sequences, as seen in plant and insect homologues. During onset of anhydrobiosis, both tps genes in A. avenae are upregulated, but exposure to cold or increased osmolarity also results in gene induction, although to a lesser extent. Trehalose seems likely therefore to play a role in a number of stress responses in nematodes.
在许多无脊椎动物的脱水生活中，非还原性二糖海藻糖的积累与耐干燥性有关，但关于这些生物中海藻糖生物合成基因的信息却很少。我们在脱水线虫燕麦真滑刃线虫中鉴定出了两个海藻糖-6-磷酸合酶（tps）基因，并确定了它们的全长cDNA序列；作为比较，还获得了模式线虫秀丽隐杆线虫的全长tps cDNA。燕麦真滑刃线虫基因编码非常相似的蛋白质，含有糖基转移酶GT-20家族特有的催化结构域，并且与秀丽隐杆线虫的tps-2最为相似；未发现燕麦真滑刃线虫中有与Ce-tps-1相对应的基因。对燕麦真滑刃线虫tps cDNA的分析揭示了几个有趣的特征，包括Aav-tps-1中剪接前导序列的可变反式剪接，以及四个不同的、新的与SL1相关的反式剪接前导序列，它们与在所有其他研究过的线虫中发现的典型SL1序列不同。后一观察结果表明，燕麦真滑刃线虫不符合在其他物种中观察到的SL1序列严格的进化保守性。在预测的线虫TPS蛋白中也注意到了不寻常的特征，这些特征将它们与其他高等真核生物（植物和昆虫）以及微生物中的同源物区分开来。系统发育分析证实了它们属于GT-20糖基转移酶家族，但表明分子进化速度加快。此外，线虫TPS蛋白具有与其他真核生物无关的N端和C端结构域：例如，线虫C端结构域不包含植物和昆虫同源物中所见的海藻糖-6-磷酸磷酸酶样序列。在脱水生活开始时，燕麦真滑刃线虫中的两个tps基因均上调，但暴露于寒冷或渗透压增加也会导致基因诱导，尽管程度较小。因此，海藻糖似乎可能在 nematodes的多种应激反应中起作用。
