Trehalose

Abstract: Trehalose is a nonreducing disaccharide in which the two glucose units are linked in an alpha,alpha-1,1-glycosidic linkage. This sugar is present in a wide variety of organisms, including bacteria, yeast, fungi, insects, invertebrates, and lower and higher plants, where it may serve as a source of energy and carbon. In yeast and plants, it may also serve as a signaling molecule to direct or control certain metabolic pathways or even to affect growth. In addition, it has been shown that trehalose can protect proteins and cellular membranes from inactivation or denaturation caused by a variety of stress conditions, including desiccation, dehydration, heat, cold, and oxidation. Finally, in mycobacteria and corynebacteria, trehalose is an integral component of various glycolipids that are important cell wall structures. There are now at least three different pathways described for the biosynthesis of trehalose. The best known and most widely distributed pathway involves the transfer of glucose from UDP-glucose (or GDP-glucose in some cases) to glucose 6-phosphate to form trehalose-6-phosphate and UDP. This reaction is catalyzed by the trehalose-P synthase (TPS here, or OtsA in Escherichia coli ). Organisms that use this pathway usually also have a trehalose-P phosphatase (TPP here, or OtsB in E. coli) that converts the trehalose-P to free trehalose. A second pathway that has been reported in a few unusual bacteria involves the intramolecular rearrangement of maltose (glucosyl-alpha1,4-glucopyranoside) to convert the 1,4-linkage to the 1,1-bond of trehalose. This reaction is catalyzed by the enzyme called trehalose synthase and gives rise to free trehalose as the initial product. A third pathway involves several different enzymes, the first of which rearranges the glucose at the reducing end of a glycogen chain to convert the alpha1,4-linkage to an alpha,alpha1,1-bond. A second enzyme then releases the trehalose disaccharide from the reducing end of the glycogen molecule. Finally, in mushrooms there is a trehalose phosphorylase that catalyzes the phosphorolysis of trehalose to produce glucose-1-phosphate and glucose. This reaction is reversible in vitro and could theoretically give rise to trehalose from glucose-1-P and glucose. Another important enzyme in trehalose metabolism is trehalase (T), which may be involved in energy metabolism and also have a regulatory role in controlling the levels of trehalose in cells. This enzyme may be important in lowering trehalose concentrations once the stress is alleviated. Recent studies in yeast indicate that the enzymes involved in trehalose synthesis (TPS, TPP) exist together in a complex that is highly regulated at the activity level as well as at the genetic level.

Abstract: counteract perturbations by urea (eg in elasmobranchs and mammalian kidney), inorganic ions, and hydrostatic pressure in deep-sea animals Trehalose and proline in overwintering insects stabilize membranes at subzero temperatures Trehalose in insects and yeast, and anionic polyols in microorganisms around hydrothermal vents, can protect proteins from denaturation by high temperatures Third, stabilizing solutes appear to be used in nature only to counteract perturbants of macromolecules, perhaps because stabilization is detrimental in the absence of perturbation Some of these solutes have applications in biotechnology, agriculture and medicine, including in vitro rescue of the misfolded protein of cystic fibrosis However, caution is warranted if high levels cause overstabilization of proteins

Abstract: Trehalose is a nonreducing disaccharide of glucose commonly found at high concentrations in anhydrobiotic organisms. In the presence of trehalose, dry dipalmitoyl phosphatidylcholine (DPPC) had a transition temperature similar to that of the fully hydrated lipid, whereas DPPC dried without trehalose had a transition temperature about 30 degrees Kelvin higher. Results obtained with infrared spectroscopy indicate that trehalose and DPPC interact by hydrogen bonding between the OH groups in the carbohydrate and the polar head groups of DPPC. These and previous results show that this hydrogen bonding alters the spacing of the polar head groups and may thereby decrease van der Waals interactions in the hydrocarbon chains of the DPPC. This interaction between trehalose and DPPC is specific to trehalose. Hence this specificity may be an important factor in the ability of this molecule to stabilize dry membranes in anhydrobiotic organisms.

Abstract: Trehalose is a nonreducing disaccharide of glucose that functions as a compatible solute in the stabilization of biological structures under abiotic stress in bacteria, fungi, and invertebrates. With the notable exception of the desiccation-tolerant “resurrection plants,” trehalose is not thought to accumulate to detectable levels in most plants. We report here the regulated overexpression of Escherichia coli trehalose biosynthetic genes (otsA and otsB) as a fusion gene for manipulating abiotic stress tolerance in rice. The fusion gene has the advantages of necessitating only a single transformation event and a higher net catalytic efficiency for trehalose formation. The expression of the transgene was under the control of either tissue-specific or stress-dependent promoters. Compared with nontransgenic rice, several independent transgenic lines exhibited sustained plant growth, less photo-oxidative damage, and more favorable mineral balance under salt, drought, and low-temperature stress conditions. Depending on growth conditions, the transgenic rice plants accumulate trehalose at levels 3–10 times that of the nontransgenic controls. The observation that peak trehalose levels remain well below 1 mg/g fresh weight indicates that the primary effect of trehalose is not as a compatible solute. Rather, increased trehalose accumulation correlates with higher soluble carbohydrate levels and an elevated capacity for photosynthesis under both stress and nonstress conditions, consistent with a suggested role in modulating sugar sensing and carbohydrate metabolism. These findings demonstrate the feasibility of engineering rice for increased tolerance of abiotic stress and enhanced productivity through tissue-specific or stress-dependent overproduction of trehalose.