Macedo-Ribeiro S, Darimont B, Sterner R, Huber R
Max-Planck Institut für Biochemie, D-82152 Martinsried, Germany.
Structure. 1996 Nov 15;4(11):1291-301. doi: 10.1016/s0969-2126(96)00137-2.
The characterization of the structural features that account for the high thermostability of some proteins is of great scientific and biotechnological interest. Proteins from hyperthermophilic organisms with optimum growth temperatures of 80 degrees C and higher generally show high intrinsic stabilities. The comparison of high resolution X-ray structures of these proteins with their counterparts from mesophilic organisms has therefore helped to identify potentially stabilizing forces in a number of cases. Small monomeric proteins which comprise only a single domain, such as ferredoxins, are especially suitable for such comparisons since the search for determinants of protein stability is considerably simplified.
The 1.75 A crystal structure of the extremely thermostable 1[4Fe-4S] ferredoxin from Thermotoga maritima (FdTm) was determined and compared with other monocluster-containing ferredoxins with different degrees of thermostability.
A comparison of the three-dimensional structure of FdTm with that of ferredoxins from mesophilic organisms suggests that the very high thermostability of FdTm is unexpectedly achieved without large changes of the overall protein structure. Instead, an increased number of potentially stabilizing features is observed in FdTm, compared with mesophilic ferredoxins. These include stabilization of alpha helices, replacement of residues in strained conformation by glycines, strong docking of the N-terminal methionine and an overall increase in the number of hydrogen bonds. Most of these features stabilize several secondary structure elements and improve the overall rigidity of the polypeptide backbone. The decreased flexibility will certainly play a relevant role in shielding the iron-sulfur cluster against physiologically high temperatures and further improve the functional integrity of FdTm.
阐明某些蛋白质具有高热稳定性的结构特征在科学和生物技术领域具有重大意义。来自最适生长温度为80摄氏度及以上的嗜热生物的蛋白质通常具有很高的内在稳定性。因此，将这些蛋白质的高分辨率X射线结构与其来自嗜温生物的对应物进行比较，在许多情况下有助于识别潜在的稳定作用力。仅由单个结构域组成的小单体蛋白质，如铁氧化还原蛋白，特别适合进行此类比较，因为寻找蛋白质稳定性的决定因素会大大简化。
测定了来自嗜热栖热菌（FdTm）的极其耐热的1[4Fe-4S]铁氧化还原蛋白的1.75埃晶体结构，并与其他具有不同热稳定性的含单簇铁氧化还原蛋白进行了比较。
将FdTm的三维结构与嗜温生物的铁氧化还原蛋白的结构进行比较表明，FdTm的极高热稳定性出乎意料地在整体蛋白质结构没有大的变化的情况下实现。相反，与嗜温铁氧化还原蛋白相比，在FdTm中观察到潜在稳定特征的数量增加。这些特征包括α螺旋的稳定、用甘氨酸取代处于应变构象的残基、N端甲硫氨酸的强对接以及氢键数量的总体增加。这些特征大多稳定了几个二级结构元件并提高了多肽主链的整体刚性。柔韧性的降低肯定会在保护铁硫簇免受生理高温影响方面发挥相关作用，并进一步提高FdTm的功能完整性。
