Katsuya Y, Sato M, Katsube Y, Matsuura Y, Tomoda K
Hyogo Prefectural Institute of Industrial Research, Kobe, Japan.
J Biol Chem. 1992 Jun 25;267(18):12668-72.
Metal ion-induced conformational changes in Serratia protease which contains one zinc ion per molecule were investigated by the small-angle x-ray scattering method. The molecule is an elongated ellipsoid of approximately 110 x 40 x 40 A with a large cleft in its central region. Comparisons of the native (zinc-enzyme) with the zinc-free (apoenzyme) enzyme and with the zinc-replated metalloenzyme show small but significant differences in their radii of gyration, maximum particle dimensions, and intraparticle pair-distance distributions. The radius of gyration and maximum particle dimension of the native enzyme are almost the same as those of the cobalt-enzyme but are shorter and longer, respectively, than those of the apo- and cadmium-enzymes. Simulation analysis based on the intraparticle pair-distribution function showed that these modified enzymes are comparable with the native enzyme in overall structure, and, except for the cobalt-enzyme, differ in cleft size. The residual enzymatic activity of the cobalt-enzyme is the same as that of the native enzyme, but the apo- and cadmium-enzymes have considerably less activity. The size of the cleft therefore is strictly controlled to ensure optimal enzyme activity, and the position and coordination behavior of the zinc ion in the cleft appears to be essential both for biological functioning and for the maintenance of the gross tertiary structure.
采用小角X射线散射法研究了每分子含有一个锌离子的粘质沙雷氏菌蛋白酶中金属离子诱导的构象变化。该分子是一个细长的椭球体，尺寸约为110×40×40埃，在其中心区域有一个大裂缝。将天然（锌酶）与无锌（脱辅基酶）酶以及锌置换金属酶进行比较，结果显示它们在回转半径、最大颗粒尺寸和颗粒内对距分布方面存在微小但显著的差异。天然酶的回转半径和最大颗粒尺寸与钴酶的几乎相同，但分别比脱辅基酶和镉酶的短和长。基于颗粒内对分布函数的模拟分析表明，这些修饰后的酶在整体结构上与天然酶相当，除了钴酶外，它们在裂缝大小上有所不同。钴酶的残余酶活性与天然酶相同，但脱辅基酶和镉酶的活性则低得多。因此，裂缝的大小受到严格控制以确保最佳酶活性，并且裂缝中锌离子的位置和配位行为对于生物功能和整体三级结构的维持似乎都是必不可少的。
