蛋白质多态解折叠行为与稳定性Ⅱ:酶的多态解折叠行为

Stability of proteins with multi-state unfolding behavior Ⅱ:Stability of enzymes with multi-state unfolding behavior

基于结构基元模型,进一步假设,由n个结构基元组成的蛋白酶,其活性中心由na(na?n)个结构基元组成,酶活性仅与组成活性中心的结构基元相关.由此,推导出适合于蛋白酶解折叠研究的变性曲线、解折叠结构基元平均自由能、物种分布等表达式.本文以盐酸胍诱导的卵清溶菌酶解折叠为例,通过荧光方法测定的溶菌酶解折叠曲线,得出卵清溶菌酶由2个结构基元组成,结构基元平均自由能<?G0element(H2O)>为48.47 kJ/mol.物种分布表明,酶活性随盐酸胍浓度的变化仅仅反映的是结构基元1(?-片结构域)的解折叠,而结构基元2(?-螺旋结构域)的解折叠反映在3.8~5.0 mol/L盐酸胍浓度范围内.结构基元模型既可描述蛋白酶多态解折叠的谱学行为,又可解释蛋白酶活性的两态性质.

Abstract： Based on the model of structural element, a new method used to study the unfolding of enzymes is presented. In this method, it was proposed that enzymes are composed of structural elements and some of them take part in the formation of active center. A least-square fitting can be used to analyze the contribution of each structural element to the enzyme. Average structural element free energy change （△Gelement（H2O）） is the probability sum of the free energy change of each structural elements. For the enzyme with multi-state unfolding behavior species fractions of enzyme are given. As example, guanidine hydrochloride induced unfolding of hen egg white lysozyme was measured by using fluorescence. The results show that lysozyme has two structural elements, structural element 2 is more stable than 1, and average structural element free energy change （AG^e! t（H20）） is 48.47 kJ/mol. The variation of enzyme activity with the concentration of guanidine hydrochloride can be attributed to the unfolding of structural element 1, β-sheet domain of lysozyme. In addition, the unfolding of structural element 2, α-helix domain of lysozyme only occurred in the range from 3.8 to 5.0 mol/L of guanidine hydrochloride. Using the model, we can study the unfolding of enzyme by not only spectral measurement, but also the measurement of enzyme activity.