Macedo-Ribeiro S, Darimont B, Sterner R
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Biol Chem. 1997 Mar-Apr;378(3-4):331-6.
Understanding the molecular mechanisms behind extreme temperature stability is of relevance for the protein folding problem and for designing proteins for industrial and medical applications. A powerful approach for understanding the structural basis of thermostability is the comparison of high resolution structures of homologous proteins from mesophiles and thermophiles. The 1.75 A crystal structure of Thermotoga maritima 1[4Fe-4S] ferredoxin was compared with those of mesophilic ferredoxins. Detailed analysis of structural differences reveals that thermostability is achieved without large changes of the overall polypeptide chain folding. The most striking differences include the formation of additional hydrogen bonding networks involving both side-chain and main-chain atoms. These networks are mainly connecting turns and strongly fix the N-terminus to the central core of the protein, increasing the overall rigidity of Thermotoga maritima ferredoxin. Other possibly stabilizing factors are the shortening of a solvent exposed surface loop, the increased content of alanines in the second alpha-helix, and the replacement of three residues close to the iron-sulfur cluster, which are in energetically unfavourable conformations in other ferredoxins, by glycines.
了解极端温度稳定性背后的分子机制对于蛋白质折叠问题以及为工业和医学应用设计蛋白质具有重要意义。理解热稳定性结构基础的一种有效方法是比较来自嗜温菌和嗜热菌的同源蛋白质的高分辨率结构。将嗜热栖热菌1[4Fe - 4S]铁氧化还原蛋白的1.75埃晶体结构与嗜温性铁氧化还原蛋白的结构进行了比较。对结构差异的详细分析表明，热稳定性的实现无需整体多肽链折叠发生大的变化。最显著的差异包括形成了涉及侧链和主链原子的额外氢键网络。这些网络主要连接转角，并将N端牢固地固定在蛋白质的中心核心，增加了嗜热栖热菌铁氧化还原蛋白的整体刚性。其他可能的稳定因素包括溶剂暴露表面环的缩短、第二个α螺旋中丙氨酸含量的增加，以及靠近铁硫簇的三个残基被甘氨酸取代，这三个残基在其他铁氧化还原蛋白中处于能量不利的构象。
