The importance of size and disorder in the cryoprotective effects of dehydrins.

Dehydrins protect plant proteins and membranes from damage during drought and cold. Vitis riparia K2 is a 48-residue protein that can protect lactate dehydrogenase from freeze-thaw damage by preventing the aggregation and denaturation of the enzyme. To further elucidate its mechanism, we used a series of V. riparia K2 concatemers (K4, K6, K8, and K10) and natural dehydrins (V. riparia YSK2, 60 kilodalton peach dehydrin [PCA60], barley dehydrin5 [Dhn5], Thellungiella salsuginea dehydrin2 [TsDHN-2], and Opuntia streptacantha dehydrin1 [OpsDHN-1]) to test the effect of the number of K-segments and dehydrin size on their ability to protect lactate dehydrogenase from freeze-thaw damage. The results show that the larger the hydrodynamic radius of the dehydrin, the more effective the cryoprotection. A similar trend is observed with polyethylene glycol, which would suggest that the protection is simply a nonspecific volume exclusion effect that can be manifested by any protein. However, structured proteins of a similar range of sizes did not show the same pattern and level of cryoprotection. Our results suggest that with respect to enzyme protection, dehydrins function primarily as molecular shields and that their intrinsic disorder is required for them to be an effective cryoprotectant. Lastly, we show that the cryoprotection by a dehydrin is not due to any antifreeze protein-like activity, as has been reported previously.