Walden H, Bell G S, Russell R J, Siebers B, Hensel R, Taylor G L
Centre for Biomolecular Sciences, The University of St Andrews, Fife, KY16 9ST, Scotland.
J Mol Biol. 2001 Mar 2;306(4):745-57. doi: 10.1006/jmbi.2000.4433.
Comparative structural studies on proteins derived from organisms with growth optima ranging from 15 to 100 degrees C are beginning to shed light on the mechanisms of protein thermoadaptation. One means of sustaining hyperthermostability is for proteins to exist in higher oligomeric forms than their mesophilic homologues. Triosephosphate isomerase (TIM) is one of the most studied enzymes, whose fold represents one of nature's most common protein architectures. Most TIMs are dimers of approximately 250 amino acid residues per monomer. Here, we report the 2.7 A resolution crystal structure of the extremely thermostable TIM from Pyrococcus woesei, a hyperthermophilic archaeon growing optimally at 100 degrees C, representing the first archaeal TIM structure. P. woesei TIM exists as a tetramer comprising monomers of only 228 amino acid residues. Structural comparisons with other less thermostable TIMs show that although the central beta-barrel is largely conserved, severe pruning of several helices and truncation of some loops give rise to a much more compact monomer in the small hyperthermophilic TIM. The classical TIM dimer formation is conserved in P. woesei TIM. The extreme thermostability of PwTIM appears to be achieved by the creation of a compact tetramer where two classical TIM dimers interact via an extensive hydrophobic interface. The tetramer is formed through largely hydrophobic interactions between some of the pruned helical regions. The equivalent helical regions in less thermostable dimeric TIMs represent regions of high average temperature factor. The PwTIM seems to have removed these regions of potential instability in the formation of the tetramer. This study of PwTIM provides further support for the role of higher oligomerisation states in extreme thermal stabilisation.
对来自生长最适温度范围为15至100摄氏度的生物体的蛋白质进行的比较结构研究，开始揭示蛋白质热适应的机制。维持超高温稳定性的一种方式是蛋白质以比其嗜温同源物更高的寡聚形式存在。磷酸丙糖异构酶（TIM）是研究最多的酶之一，其折叠结构代表了自然界中最常见的蛋白质结构之一。大多数TIM是每个单体约250个氨基酸残基的二聚体。在此，我们报告了来自沃氏嗜热栖热菌（一种在100摄氏度下生长最佳的超嗜热古菌）的极其耐热的TIM的2.7埃分辨率晶体结构，这是首个古菌TIM结构。沃氏嗜热栖热菌TIM以四聚体形式存在，其单体仅由228个氨基酸残基组成。与其他耐热性较低的TIM的结构比较表明，尽管中央β桶在很大程度上是保守的，但几个螺旋的严重修剪和一些环的截断导致超嗜热小TIM中的单体更加紧凑。经典的TIM二聚体形成在沃氏嗜热栖热菌TIM中是保守的。沃氏嗜热栖热菌TIM的极端耐热性似乎是通过形成一个紧凑的四聚体来实现的，其中两个经典的TIM二聚体通过广泛的疏水界面相互作用。四聚体主要通过一些修剪后的螺旋区域之间的疏水相互作用形成。耐热性较低的二聚体TIM中的等效螺旋区域代表平均温度因子较高的区域。沃氏嗜热栖热菌TIM似乎在四聚体形成过程中去除了这些潜在不稳定区域。对沃氏嗜热栖热菌TIM的这项研究为更高寡聚化状态在极端热稳定中的作用提供了进一步支持。
