Empadinhas Nuno, da Costa Milton S
Department of Biochemistry, Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal.
Syst Appl Microbiol. 2008 Aug;31(3):159-68. doi: 10.1016/j.syapm.2008.05.002. Epub 2008 Jul 2.
Mannosylglycerate (MG) is an intracellular organic solute found in some red algae, and several thermophilic bacteria and hyperthermophilic archaea. Glucosylglycerate (GG) was identified at the reducing end of a polysaccharide from mycobacteria and in a free form in a very few mesophilic bacteria and halophilic archaea. MG has a genuine role in the osmoadaptation and possibly in thermal protection of many hyper/thermophilic bacteria and archaea, but its role in red algae, where it was identified long before hyperthermophiles were even known to exist, remains to be clarified. The GG-containing polysaccharide was initially detected in Mycobacterium phlei and found to regulate fatty acid synthesis. More recently, GG has been found to be a major compatible solute under salt stress and nitrogen starvation in a few microorganisms. This review summarizes the occurrence and physiology of MG accumulation, as well as the distribution of GG, as a free solute or associated with larger macromolecules. We also focus on the recently identified pathways for the synthesis of both molecules, which were elucidated by studying hyper/thermophilic MG-accumulating organisms. The blooming era of genomics has now allowed the detection of these genes in fungi and mosses, opening a research avenue that spans the three domains of life, into the role of these two sugar derivatives.
甘露糖基甘油酸（MG）是一种细胞内有机溶质，存在于一些红藻、几种嗜热细菌和超嗜热古菌中。葡萄糖基甘油酸（GG）在分枝杆菌多糖的还原端被鉴定出来，并且在极少数嗜温细菌和嗜盐古菌中以游离形式存在。MG在许多嗜热/超嗜热细菌和古菌的渗透适应以及可能的热保护中具有重要作用，但其在红藻中的作用仍有待阐明，红藻中MG的发现远早于嗜热微生物的发现。含GG的多糖最初在草分枝杆菌中被检测到，并发现其可调节脂肪酸合成。最近，在一些微生物中发现GG是盐胁迫和氮饥饿条件下的主要相容性溶质。本综述总结了MG积累的发生情况和生理学，以及GG作为游离溶质或与较大大分子相关的分布情况。我们还重点关注了最近通过研究嗜热/超嗜热MG积累生物阐明的这两种分子的合成途径。基因组学的蓬勃发展现在使我们能够在真菌和苔藓中检测到这些基因，从而开辟了一条跨越生命三个域的研究途径，以探究这两种糖衍生物的作用。
