Cold-active structure of the psychrophile enzymes

为了研究酶冷适应的分子基础，我们测定了嗜冷希瓦氏菌K14-2中色氨酸合成酶α亚基的晶体结构，并对其理化性质进行了研究。亲冷酶的耐热稳定性和变性稳定性较低的原因是其展开速率较快，再折叠速率较慢。酶变性的两态转变是高度协同的。与其他物种的色氨酸合成酶相比，该嗜冷酶的空腔体积增加，离子对数量减少。这种酶在与催化功能有关的环附近也缺少一个氢键。这些特性可能提供了在低温下催化活性所需的构象灵活性。

To investigate the molecular basis of cold adaptation of enzymes, we determined the crystal structure of the tryptophan synthase alpha subunit from the psychrophile Shewanella frigidimarina K14-2 and also examined its physicochemical properties. The lower stabilities against heat and denaturant of the psychrophile enzyme originated from both a faster unfolding rate and a slower refolding rate. The two-state transition of denaturation for the enzyme was highly cooperative. Relative to tryptophan synthases from other species, the psychrophile enzyme exhibited an increase in cavity volume and a decrease in the number of ion pairs. The enzyme also lacks a hydrogen bond near a loop related to catalytic function. These characteristics of the psychrophile enzyme might provide the conformational flexibility required for catalytic activity at low temperatures.