Centro de Neurociências e Biologia Celular, Universidade de Coimbra, 3004-517 Coimbra, Portugal.
J Bacteriol. 2010 Mar;192(6):1624-33. doi: 10.1128/JB.01424-09. Epub 2010 Jan 8.
The compatible solute mannosylglucosylglycerate (MGG), recently identified in Petrotoga miotherma, also accumulates in Petrotoga mobilis in response to hyperosmotic conditions and supraoptimal growth temperatures. Two functionally connected genes encoding a glucosyl-3-phosphoglycerate synthase (GpgS) and an unknown glycosyltransferase (gene Pmob_1143), which we functionally characterized as a mannosylglucosyl-3-phosphoglycerate synthase and designated MggA, were identified in the genome of Ptg. mobilis. This enzyme used the product of GpgS, glucosyl-3-phosphoglycerate (GPG), as well as GDP-mannose to produce mannosylglucosyl-3-phosphoglycerate (MGPG), the phosphorylated precursor of MGG. The MGPG dephosphorylation was determined in cell extracts, and the native enzyme was partially purified and characterized. Surprisingly, a gene encoding a putative glucosylglycerate synthase (Ggs) was also identified in the genome of Ptg. mobilis, and an active Ggs capable of producing glucosylglycerate (GG) from ADP-glucose and d-glycerate was detected in cell extracts and the recombinant enzyme was characterized, as well. Since GG has never been identified in this organism nor was it a substrate for the MggA, we anticipated the existence of a nonphosphorylating pathway for MGG synthesis. We putatively identified the corresponding gene, whose product had some sequence homology with MggA, but it was not possible to recombinantly express a functional enzyme from Ptg. mobilis, which we named mannosylglucosylglycerate synthase (MggS). In turn, a homologous gene from Thermotoga maritima was successfully expressed, and the synthesis of MGG was confirmed from GDP-mannose and GG. Based on the measurements of the relevant enzyme activities in cell extracts and on the functional characterization of the key enzymes, we propose two alternative pathways for the synthesis of the rare compatible solute MGG in Ptg. mobilis.
相容溶质甘露糖基葡萄糖基甘油(MGG)最近在 Petrotoga miotherma 中被发现,也会在 Petrotoga mobilis 中积累,以应对高渗条件和超最佳生长温度。在 Ptg. mobilis 的基因组中鉴定了两个功能上相互连接的基因,编码葡萄糖基-3-磷酸甘油酸合酶(GpgS)和一种未知的糖基转移酶(基因 Pmob_1143),我们将其功能表征为甘露糖基葡萄糖基-3-磷酸甘油酸合酶,并将其命名为 MggA。该酶利用 GpgS 的产物葡萄糖基-3-磷酸甘油酸(GPG)以及 GDP-甘露糖来产生甘露糖基葡萄糖基-3-磷酸甘油酸(MGPG),这是 MGG 的磷酸化前体。在细胞提取物中测定了 MGPG 的去磷酸化,并且对天然酶进行了部分纯化和表征。令人惊讶的是,在 Ptg. mobilis 的基因组中还鉴定了一个编码假定的葡萄糖基甘油酸合酶(Ggs)的基因,并且在细胞提取物和重组酶中检测到能够从 ADP-葡萄糖和 D-甘油酸产生葡萄糖基甘油酸(GG)的活性 Ggs。由于 GG 在该生物体中从未被鉴定过,也不是 MggA 的底物,我们预计 MGG 合成存在非磷酸化途径。我们推测鉴定了相应的基因,其产物与 MggA 具有一些序列同源性,但无法从 Ptg. mobilis 中重组表达功能酶,我们将其命名为甘露糖基葡萄糖基甘油酸合酶(MggS)。反过来,从 Thermotoga maritima 成功表达了同源基因,并从 GDP-甘露糖和 GG 确认了 MGG 的合成。基于细胞提取物中相关酶活性的测量和关键酶的功能表征,我们提出了 Ptg. mobilis 中稀有相容溶质 MGG 合成的两种替代途径。