title: To be or not to be a compatible solute: bioversatility of mannosylglycerate and glucosylglycerate.
abstract: 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.
authors.affiliation: Department of Biochemistry, Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal.
authors.forename: Nuno
authors.initials: N
authors.lastname: Empadinhas
authors.forename: Milton S
authors.initials: MS
authors.lastname: da Costa
mesh_terms: D000222:Adaptation, Physiological; D001105:Archaea / Q000145:classification / Q000502:physiology; D001419:Bacteria / Q000145:classification / Q000378:metabolism; D018407:Bacterial Physiological Phenomena; D005658:Fungi / Q000378:metabolism; D005960:Glucosides / Q000096:biosynthesis* / Q000737:chemistry; D005988:Glyceric Acids / Q000737:chemistry; D006358:Hot Temperature; D008358:Mannose / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000737:chemistry; D009994:Osmolar Concentration; D000461:Rhodophyta / Q000378:metabolism
chemical_list: C509251:2-glucosylglycerate; D005960:Glucosides; D005988:Glyceric Acids; C402688:mannosylglycerate; D008358:Mannose