alpha, alpha-Trehalose (trehalose) is a nonreducing disaccharide of glucose and is accumulated at high concentrations
in some anhydrobiotic organisms, which can survive without water for long periods and rapidly resume active
metabolism upon hydration. Although it has been proposed that the intriguing mechanism of bioprotection in
anhydrobiosis is conferred by a water channel, details of such a channel have yet to be revealed. We determined
the crystal structure of a trehalose anhydrate to further understand the relationship between the structure of
water channels and the trehalose polymorph. The space group was identical to that of the dihydrate and the
lattice constants were also very similar. Among the five intermolecular hydrogen bonds between the trehalose
molecules, four were preserved in the anhydrate. If dehydration of the dihydrate is slow and/or gentle enough
to preserve the hydrogen bonds, transformation from the dihydrate to the anhydrate may occur. There are
two different holes, hole-1 and hole-2, along one crystal axis. Hole-1 is constructed by trehalose molecules
with a screw diad at its center, while hole-2 has a smaller diameter and is without a symmetry operator.
Because of the screw axis at the center of hole-1, hollows are present at the side of the hole with diameters
roughly equal to that of hole-1. Hole-1 and side pockets followed by hollows correspond to the positions of
two water molecules of the dihydrate. The side hollows of the water channel are also observed in the waterfilled
hole of the dihydrate. Consequently, hole-1 is considered to be a one-dimensional water channel with
side pockets. We also calculated molecular and crystal energies to examine the rapid water uptake of the
anhydrate. It was demonstrated that the intermolecular interactions in the anhydrate were weaker than in the
other anhydrous form, and probably also than those in amorphous trehalose. The anhydrate provides water
capture for another solid form and gives protection from water uptake. These structural properties of the
anhydrate may elucidate bioprotection in anhydrobiosis.
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