Papaleo Elena, Olufsen Magne, De Gioia Luca, Brandsdal Bjørn O
The Norwegian Structural Biology Centre, Department of Chemistry, University of Tromsø, N9037 Tromsø, Norway.
J Mol Graph Model. 2007 Jul;26(1):93-103. doi: 10.1016/j.jmgm.2006.09.012. Epub 2006 Sep 30.
Adaptation to both high and low temperatures requires proteins with special properties. While organisms living at or close to the boiling point of water need to have proteins with increased stability, other properties are required at temperatures close to the freezing point of water. Indeed, it has been shown that enzymes adapted to cold environments are less resistant to heat with a concomitant increased activity as compared to their warm-active counter-parts. Several recent studies have pointed in the direction that electrostatic interactions play a central role in temperature adaptation, and in this study we investigate the role such interactions have in adaptation of elastase from Atlantic salmon and pig. Molecular dynamics (MD) simulations have been used to generate structural ensembles at 283 and 310 K of the psychrophilic and mesophilic elastase, and a total of eight 12 ns simulations have been carried out. Even though the two homologues have a highly similar three-dimensional structure, the location and number of charged amino acids are very different. Based on the simulated structures we find that very few salt-bridges are stable throughout the simulations, and provide little stabilization/destabilization of the proteins as judged by continuum electrostatic calculations. However, the mesophilic elastase is characterized by a greater number of salt-bridges as well as a putative salt-bridge network close to the catalytic site, indicating a higher rigidity of the components involved in the catalytic cycle. In addition, subtle differences are also found in the electrostatic potentials in the vicinity of the catalytic residues, which may explain the increased catalytic efficiency of the cold-adapted elastase.
适应高温和低温都需要具有特殊性质的蛋白质。生活在或接近水沸点的生物体需要具有更高稳定性的蛋白质，而在接近水冰点的温度下则需要其他性质的蛋白质。事实上，已有研究表明，与适应温暖环境的对应酶相比，适应寒冷环境的酶对热的耐受性较低，但活性相应增加。最近的几项研究指出，静电相互作用在温度适应中起着核心作用，在本研究中，我们调查了这种相互作用在大西洋鲑鱼和猪的弹性蛋白酶适应过程中的作用。分子动力学（MD）模拟已用于生成嗜冷和嗜温弹性蛋白酶在283 K和310 K时的结构系综，总共进行了八次12 ns的模拟。尽管这两种同源物具有高度相似的三维结构，但带电荷氨基酸的位置和数量却有很大差异。基于模拟结构，我们发现在整个模拟过程中很少有盐桥是稳定的，根据连续静电计算判断，它们对蛋白质的稳定/不稳定作用很小。然而，嗜温弹性蛋白酶的特点是盐桥数量更多，并且在催化位点附近有一个假定的盐桥网络，这表明参与催化循环的组分具有更高的刚性。此外，在催化残基附近的静电势中也发现了细微差异，这可能解释了冷适应弹性蛋白酶催化效率的提高。
