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Protein misfolding, aggregation and deposition in the brain, in the form of amyloid, are implicated in the etiology of several neurodegenerative disorders, such as Alzheimer's, Parkinson's and prion diseases. Drugs available on the market reduce the symptoms, but they are not a cure. Therefore, it is urgent to identify promising targets and develop effective drugs. Preservation of protein native conformation and/or inhibition of protein aggregation seem pertinent targets for drug development. Several studies have shown that organic solutes, produced by extremophilic microorganisms in response to osmotic and/or heat stress, prevent denaturation and aggregation of model proteins. Among these stress solutes, mannosylglycerate, mannosylglyceramide, di- myo-inositol phosphate, diglycerol phosphate and ectoine are effective in preventing amyloid formation by Alzheimer's Aβ peptide and/or α-synuclein in vitro. Moreover, mannosylglycerate is a potent inhibitor of Aβ and α-synuclein aggregation in living cells, and mannosylglyceramide and ectoine inhibit aggregation and reduce prion peptide-induced toxicity in human cells. This review focuses on the efficacy of stress solutes from hyper/thermophiles and ectoines to prevent amyloid formation in vitro and in vivo and their potential application in drug development against protein misfolding diseases. Current and envisaged applications of these extremolytes in neurodegenerative diseases and healthcare will also be addressed. [ABSTRACT FROM AUTHOR]

Halophilic and halotolerant microorganisms adapted to thrive in hot environments accumulate compatible solutes that usually have a negative charge either associated with a carboxylic group or a phosphodiester unit. Mannosylglycerate (MG) has been detected in several members of (hyper)thermophilic bacteria and archaea, in which it responds primarily to osmotic stress. The outstanding ability of MG to stabilize protein structure in vitro as well as in vivo has been convincingly demonstrated. These findings led to an increasingly supported link between MG and microbial adaptation to high temperature. However, the accumulation of MG in many red algae has been known for a long time, and the peculiar distribution of MG in such distant lineages was intriguing. Knowledge on the biosynthetic machinery together with the rapid expansion of genome databases allowed for structural and phylogenetic analyses and provided insight into the distribution of MG. The two pathways for MG synthesis have distinct evolutionary histories and physiological roles: in red algae MG is synthesised exclusively via the single-step pathway and most probably is unrelated with stress protection. In contrast, the two-step pathway is strongly associated with osmoadaptation in (hyper)thermophilic prokaryotes. The phylogenetic analysis of the two-step pathway also reveals a second cluster composed of fungi and mesophilic bacteria, but MG has not been demonstrated in members of this cluster; we propose that the synthase is part of a more complex pathway directed at the synthesis of yet unknown molecules containing the mannosyl-glyceryl unit. [ABSTRACT FROM AUTHOR]

We disrupted the mpgS encoding mannosyl-3-phosphoglycerate synthase (MpgS) of Thermus thermophilus strains HB27 and RQ-1, by homologous recombination, to assess the role of the compatible solute mannosylglycerate (MG) in osmoadaptation of the mutants, to examine their ability to grow in NaCl-containing medium and to identify the intracellular organic solutes. Strain HB27 accumulated only MG when grown in defined medium containing 2% NaCl; mutant HB27M9 did not grow in the same medium containing more than 1% NaCl. When trehalose or MG was added, the mutant was able to grow up to 2% of NaCl and accumulated trehalose or MG, respectively, plus amino acids. T. thermophilus RQ-1 grew in medium containing up to 5% NaCl, accumulated trehalose and lower amounts of MG. Mutant RQ-1M1 lost the ability to grow in medium containing more than 3% NaCl and accumulated trehalose and moderate levels of amino acids. Exogenous MG did not improve the ability of the organism to grow above 3% NaCl, but caused a decrease in the levels of amino acids. Our results show that MG serves as a compatible solute primarily during osmoadaptation at low levels of NaCl while trehalose is primarily involved in osmoadaptation during growth at higher NaCl levels. [ABSTRACT FROM AUTHOR]

The thermophilic and halotolerant nature of Rubrobacter xylanophilus led us to investigate the accumulation of compatible solutes in this member of the deepest lineage of the Phylum Actinobacteria. Trehalose and mannosylglycerate (MG) were the major compounds accumulated under all conditions examined, including those for optimal growth. The addition of NaCl to a complex medium and a defined medium had a slight or negligible effect on the accumulation of these compatible solutes. Glycine betaine, di- myo-inositol-phosphate (DIP), a new phosphodiester compound, identified as di- N-acetyl-glucosamine phosphate and glutamate were also detected but in low or trace levels. DIP was always present, except at the highest salinity examined (5% NaCl) and at the lowest temperature tested (43°C). Nevertheless, the levels of DIP increased with the growth temperature. This is the first report of MG and DIP in an actinobacterium and includes the identification of the new solute di- N-acetyl-glucosamine phosphate. [ABSTRACT FROM AUTHOR]

The protection of mannosylglycerate, at 0.5 M concentration, against heat inactivation of the model enzyme lactate dehydrogenase (LDH) was compared to that exerted by other compatible solutes, namely, trehalose, ectoine, hydroxyectoine, di-myo-inositol phosphate, diglycerol phosphate, and mannosylglyceramide. Mannosylglycerate and hydroxyectoine were the best stabilizers of the enzyme and showed comparable protective effects. Diglycerol phosphate, trehalose, and mannosylglyceramide protected the enzyme to a lower extent. Ectoine conferred no protection, and di-myo-inositol phosphate had a strong destabilizing effect. The superior ability of mannosylglycerate to prevent LDH inactivation was accompanied by a higher efficiency in preventing LDH aggregation induced by heat stress. Moreover, mannosylglycerate induced an increase of 4.5°C in the melting temperature of LDH, whereas the same molar concentration of trehalose caused an increase of only 2.2°C. The effectiveness of mannosylglycerate in protecting LDH was also compared to that of other chemically related compounds: mannose, methyl-mannoside, potassium glycerate, glucosylglycerol, glycerol, and glucose. Mannosylglycerate conferred the highest protection, but glucosylglycerol and potassium glycerate were very efficient; glucose exerted a low degree of protection, glycerol and methyl-mannoside had no significant effect, and mannose caused destabilization. Mannosylglycerate was also a good thermoprotectant of glucose oxidase from Aspergillus niger, an enzyme with a net charge opposite to that of LDH under the working conditions. Given the superior performance of mannosylglycerate as a thermoprotectant of enzyme activity in vitro, it is conceivable that it also fulfills a protein thermoprotective function in vivo. [ABSTRACT FROM AUTHOR]