The K2 Dehydrin: An Intrinsically Disordered Membrane Protector

Dehydrins are disordered plant proteins which are expressed when the plant is exposed to stresses such as drought, high salinity, and low temperatures. Cell membranes appear to be the primary site of injury, and dehydrins interact with membranes in vitro and in vivo, often exerting a protective effect. K2 dehydrin from Vitis riparia provides an opportunity to study the protective effect of K-segment binding on membrane surfaces. Liposome fusion assays indicate that K2 attenuates freeze-thaw-induced damage in PC/PA membranes. This effect is not a result of significant coverage of the membrane surface, since merocyanine 540 accessibility is unaffected. Protection is also not a result of microviscosity change in the hydrophobic interior or the water-phospholipid interface of PC/PA membranes. Differential scanning calorimetry experiments indicate that K2 reduces the thermotropic phase transition temperature of 1,2-dimyristoyl-sn-glycero-3-phosphate/1,2-dimyristoyl-sn-glycero-3-phosphocholine membranes by 3°C. This effect might be due to increased hydration of phosphate head groups by K2.