Li Daixi, He Xiaoming
Department of Mechanical Engineering, and Biomedical Engineering Program, University of South Carolina, Columbia, South Carolina 29208, USA.
Biomacromolecules. 2009 Jun 8;10(6):1469-77. doi: 10.1021/bm9002688.
Late embryogenesis abundant (LEA) proteins have been found in a number of anhydrobiotic (i.e., a state of anhydrobiosis or life without water) organisms that are adapted to severe water deficit as a result of extreme drought and cold in nature. However, the precise mechanism by which LEA proteins protect the organisms in response to water depletion remains to be defined. Because protein functions are generally determined by its structure, molecular dynamics simulations were performed in this study to understand the structure and its stability of a 66-amino acid fragment of a group 3 LEA protein from an anhydrobiotic nematode during desiccation. It was found that, unlike the vast majority of proteins, the fully hydrated LEA protein in an aqueous solution is by and large unstructured (mainly in the form of random coils and turns). The protein gradually becomes folded into a hairpin-like, double-bundled, alpha-helical 3D conformation in response to the loss of water. Major structural formation was observed to occur only when the water content is less than about 20 wt %. It was further found the protein structure and its stability during desiccation are determined primarily by hydrogen bonding interactions followed by electrostatic interactions, both of which are a result of the extremely hydrophilic nature of the LEA protein. The Lennard-Jones interactions (van der Waals interactions) are the least important in determining the protein structure and its stability during water deficit.
晚期胚胎发生丰富（LEA）蛋白已在许多耐脱水生物（即处于脱水状态或无水生存状态）中被发现，这些生物因自然界中的极端干旱和寒冷而适应了严重的水分亏缺。然而，LEA蛋白响应水分缺失保护生物体的确切机制仍有待确定。由于蛋白质功能通常由其结构决定，因此本研究进行了分子动力学模拟，以了解一种来自耐脱水线虫的3组LEA蛋白的66个氨基酸片段在脱水过程中的结构及其稳定性。研究发现，与绝大多数蛋白质不同，水溶液中完全水合的LEA蛋白基本上是无结构的（主要呈无规卷曲和转角形式）。随着水分的流失，该蛋白逐渐折叠成发夹状、双束状的α螺旋三维构象。仅当含水量低于约20 wt%时才观察到主要结构的形成。进一步发现，脱水过程中该蛋白的结构及其稳定性主要由氢键相互作用决定，其次是静电相互作用，这两者都是LEA蛋白极强亲水性的结果。在水分亏缺期间， Lennard-Jones相互作用（范德华相互作用）在决定蛋白质结构及其稳定性方面最不重要。
