Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Protein Sci. 2011 Jan;20(1):42-50. doi: 10.1002/pro.534.
Dehydration proteins (Dehydrins) are expressed during dehydration stress in plants and are thought to protect plant proteins and membranes from the loss of water during drought and at cold temperatures. Several different dehydrins have been shown to protect lactate dehydrogenase (LDH) from damage from being frozen and thawed. We show here that a 48 residue K₂ dehydrin from Vitis riparia protects LDH more effectively than bovine serum albumin, a protein with known cryoprotective function. Light scattering and 8-anilino-1-naphthalene sulfonate fluorescence experiments show that dehydrins prevent aggregation and unfolding of the enzyme. The cryoprotective effects of LDH are reduced by the addition of salt, suggesting that the positively charged K-segments are attracted to a negatively charged surface but this does not result in binding. Overall K₂ is an intrinsically disordered protein; nuclear magnetic resonance relaxation experiments indicate that the two-terminal, Lys-rich K-segments show a weak propensity for α-helicity and are flexible, and that the central, polar rich phi-segment has no secondary structure preference and is highly flexible. We propose that the phi-segments in dehydrins are important for maintaining the disordered structure so that the protein can act as a molecular shield to prevent partially denatured proteins from interacting with one another, whereas the K-segments may help to localize the dehydrin near the enzyme surface.
脱水蛋白（脱水素）在植物脱水胁迫期间表达，被认为可以保护植物蛋白和膜免受干旱和低温下水分流失的影响。已经证明几种不同的脱水素可以保护乳酸脱氢酶（LDH）免受冷冻和解冻的损伤。我们在这里表明，来自葡萄 riparia 的 48 个残基 K₂脱水素比具有已知冷冻保护功能的牛血清白蛋白更有效地保护 LDH。光散射和 8-苯胺-1-萘磺酸荧光实验表明，脱水素可以防止酶的聚集和展开。LDH 的冷冻保护作用会因加盐而降低，这表明带正电荷的 K 段会被带负电荷的表面吸引，但这并不会导致结合。总体而言，K₂ 是一种固有无序的蛋白质；核磁共振弛豫实验表明，两个末端富含赖氨酸的 K 段具有较弱的α螺旋倾向和灵活性，而中央富含极性的 phi 段没有二级结构偏好，非常灵活。我们提出，脱水素中的 phi 段对于维持无定形结构很重要，以便该蛋白可以作为分子盾牌，防止部分变性的蛋白相互作用，而 K 段可能有助于将脱水素定位在酶表面附近。
