Georlette Daphné, Damien Benjamin, Blaise Vinciane, Depiereux Eric, Uversky Vladimir N, Gerday Charles, Feller Georges
Laboratory of Biochemistry, Institute of Chemistry B6, University of Liège, B-4000 Liège, Belgium.
J Biol Chem. 2003 Sep 26;278(39):37015-23. doi: 10.1074/jbc.M305142200. Epub 2003 Jul 10.
Psychrophiles, host of permanently cold habitats, display metabolic fluxes comparable to those exhibited by mesophilic organisms at moderate temperatures. These organisms have evolved by producing, among other peculiarities, cold-active enzymes that have the properties to cope with the reduction of chemical reaction rates induced by low temperatures. The emerging picture suggests that these enzymes display a high catalytic efficiency at low temperatures through an improved flexibility of the structural components involved in the catalytic cycle, whereas other protein regions, if not implicated in catalysis, may be even more rigid than their mesophilic counterparts. In return, the increased flexibility leads to a decreased stability of psychrophilic enzymes. In order to gain further advances in the analysis of the activity/flexibility/stability concept, psychrophilic, mesophilic, and thermophilic DNA ligases have been compared by three-dimensional-modeling studies, as well as regards their activity, surface hydrophobicity, structural permeability, conformational stabilities, and irreversible thermal unfolding. These data show that the cold-adapted DNA ligase is characterized by an increased activity at low and moderate temperatures, an overall destabilization of the molecular edifice, especially at the active site, and a high conformational flexibility. The opposite trend is observed in the mesophilic and thermophilic counterparts, the latter being characterized by a reduced low temperature activity, high stability and reduced flexibility. These results strongly suggest a complex relationship between activity, flexibility and stability. In addition, they also indicate that in cold-adapted enzymes, the driving force for denaturation is a large entropy change.
嗜冷菌是永久寒冷栖息地的宿主，其代谢通量与中温生物在适度温度下表现出的代谢通量相当。这些生物通过产生多种特性，其中包括具有应对低温引起的化学反应速率降低特性的冷活性酶而进化。新出现的情况表明，这些酶通过提高催化循环中涉及的结构成分的灵活性，在低温下表现出高催化效率，而其他蛋白质区域（如果不参与催化）可能比它们的中温对应物更刚性。作为回报，增加的灵活性导致嗜冷酶的稳定性降低。为了在活性/灵活性/稳定性概念的分析上取得进一步进展，通过三维建模研究比较了嗜冷、中温和嗜热DNA连接酶，以及它们的活性、表面疏水性、结构通透性、构象稳定性和不可逆热解折叠。这些数据表明，冷适应DNA连接酶的特征是在低温和中温下活性增加、分子结构整体不稳定，尤其是在活性位点，以及高构象灵活性。在中温和嗜热对应物中观察到相反的趋势，后者的特征是低温活性降低、稳定性高和灵活性降低。这些结果有力地表明了活性、灵活性和稳定性之间的复杂关系。此外，它们还表明，在冷适应酶中，变性的驱动力是大的熵变。
