Proline hydration at low temperatures: its role in the protection of cell from freeze-induced stress.

The natural amino acid L-α-proline (Pro) is a compatible osmolyte which accumulates in the cell cytoplasm to protect structure and function of various proteins and enzymes under abiotic stress, like for instance, freezing. It is assumed that the interactions of Pro with intracellular water play an important role in the protection mechanism. However, until now the details of these interactions are far from being fully understood. We present results of a theoretical study of the hydration of Pro zwitterion (Pro-ZW) in water in the temperature range of 298-248 K. The data were obtained by the integral equation method in the framework of the 1D- and 3D-RISM approaches. The structural data were analyzed in terms of radial and spatial distribution functions. The observed features of Pro-ZW hydration are discussed from the position of the biological role of Pro as a cryoprotectant. In particular, it was found that under cooling conditions this protectant is able to bind a significant amount of water molecules and, thus, is helping to keep water inside the cell.