Molecular Dynamics Studies of the Hydration of R,R-Trehalose Qiang Liu, † R. K. Schmidt, †,‡ B. Teo, † P. A. Karplus, § and J. W. Brady* ,† Contribution from the Department of Food Science, Stocking Hall, and Section of Biochemistry, Molecular and Cell Biology, Biotechnology Building, Cornell UniVersity, Ithaca, New York 14853 ReceiVed March 12, 1997. ReVised Manuscript ReceiVed May 19, 1997 X Abstract: Molecular dynamics simulations have been used to model the aqueous solvation of the nonreducing sugar R,R-trehalose. The anisotropic structuring of water around the trehalose molecule was calculated in a Cartesian coordinate frame fixed with respect to the sugar molecule by averaging water positions over the trajectories and was plotted in two and three dimensions relative to the sugar. The hydrogen bonding of this sugar to solvent was calculated and compared to other sugar solutes. Hydration was required to produce the experimental conformation, through the exchange of an internal hydrogen bond for similar bonds to solvent. This equilibrium conformation was found to impose extensive structuring on the adjacent solvent, with structuring extending out to at least the third “solvation shell”, while pure liquid water exhibits such structure only in its nearest neighbors. The details of the structuring are determined by both the specific stereochemical topology of the molecule and its conformation, with considerable interplay between conformation and solvent structure. The effect of solute flexibility on the application of this solvent density mapping technique was also examined. While the extensive solvent structural perturbation induced by the solute suggests why the sugars in general are useful antidessicants and cryoprotectants, trehalose does not appear from these results to be unique in its solvation properties. In addition, the results are consistent with the suggestion that much of the effectiveness of trehalose could result from its direct binding to biological membranes and proteins rather than from unique solution properties. I. Introduction With their large number of hydrogen-bonding hydroxyl groups, carbohydrates might be expected to interact strongly with water. In general, the solvation properties of the carbo- hydrates are a function of the specific stereochemical arrange- ment of the hydroxyl groups of each molecule, and each sugar solution will have distinct properties, 1 even for stereoisomers differing in structure at only one asymmetric carbon. The structural details of a carbohydrate can determine how it interacts with solvent water molecules in ways which are not yet completely understood. Sugars are generally thought of as net “structure-makers”, 2 meaning that they impose a collective structure on the adjacent solvent different from that which it would otherwise adopt. While it is sometimes possible to characterize such solvent structuring from diffraction studies of hydrated crystals of biological molecules, 3,4 it has been much more difficult to determine the details of solvent structure in dilute liquid solutions, particularly for non-spherically-symmetric molecular solutes. 5 The consequences of such structuring, however, are quite important in determining a number of physical properties of carbohydrate solutions. Organisms exploit the water-structuring characteristics of the different sugars in a variety of ways, such as to modify the viscosity of cellular fluids and to protect against freezing or dehydration. 6,7 Determining how molecular structures affect solution properties would be of general utility in understanding biopolymer systems and could have practical applications, as in the design of novel cryo- protectants. The trehaloses are a family of nonreducing disaccharides that result from the combination of two D-glucopyranose molecules through (1f1) glycosidic linkages. Three such dimers are possible, R,R, R,, and ,, indicating the linkage configurations. The R,R-trehalose dimer (Figure 1a), which hereafter will simply be referred to as “trehalose”, occurs in significant amounts in certain plants, seeds, and invertebrates adapted to endure drought, 8,9 and it has been shown that this disaccharide is able to stabilize proteins and lipid bilayers in Vitro during dehydra- tion. Several mechanisms for the antidessicant properties of trehalose have been advanced. Trehalose solutions have the highest glass transition temperature of any of the disaccha- rides, 7,8,10 suggesting that the ability of trehalose to stabilize biological systems is related to its ability to control water mobility by forming a glassy state. It has also been proposed that the stabilizing effect may result from direct interactions of the disaccharide with proteins and phospholipid head groups, 11 perhaps replacing hydrogen-bonded solvent molecules. In part because of its potential practical applications in cryobiology, trehalose has been studied extensively, 6,7,12-17 but * Author to whom correspondence should be addressed. † Department of Food Science. ‡ Present Address: Division of Biochemistry and Molecular Biology, John Curtin School of Medical Research, Australian National University, Canberra, ACT 0200, Australia. § Section of Biochemistry, Molecular and Cell Biology. X Abstract published in AdVance ACS Abstracts, August 1, 1997. (1) Goldberg, R. N.; Tewari, Y. B. J. Phys. Chem. Ref. Data 1989, 18, 809-880. (2) Walrafen, G. E.; Fisher, M. R. Methods Enzymol. 1986, 127, 91- 105. (3) Karplus, P. A.; Faerman, C. Curr. Opin. Struct. Biol. 1994, 4, 770- 776. (4) Jeffrey, G. A.; Huang, D.-B. Carbohydr. Res. 1990, 206, 173-182. (5) Soper, A. K. J. Chem. Phys. 1994, 101, 6888-6901. (6) Koster, K. L.; Leopold, A. C. Plant Physiol. 1988, 88, 829-832. (7) Green, J. L.; Angell, C. A. J. Phys. Chem. 1989, 93, 2880-2882. (8) Crowe, L. M.; Reid, D. S.; Crowe, J. H. Biophys. J. 1996, 71, 2087- 2093. (9) Weisburd, S. Sci. News 1988, 133, 97-112. (10) Ding, S.-P.; Fan, J.; Green, J. L.; Lu, Q.; Sanchez, E.; Angell, C. A. J. Thermal Anal. 1996, 47, 1391-1405. (11) Crowe, J. H.; Crowe, L. M.; Chapman, D. Science 1984, 223, 701- 703. (12) Bock, K.; Defaye, J.; Driguez, H.; Bar-Guilloux, E. Eur. J. Biochem. 1983, 131, 595-600. (13) Ram, P.; Mazzola, L.; Prestegard, J. H. J. Am. Chem. Soc. 1989, 111, 3176-3182. (14) Duda, C. A.; Stevens, E. S. J. Am. Chem. Soc. 1990, 112, 7406. (15) Gaffney, S. H.; Haslam, E.; Lilley, T. H.; Ward, T. R. J. Chem. Soc., Faraday Trans. 1 1988, 84, 2545-2552. 7851 J. Am. Chem. Soc. 1997, 119, 7851-7862 S0002-7863(97)00798-1 CCC: $14.00 © 1997 American Chemical Society