【摘要】 在细菌、真菌及植物中,分支酸是一种位于关键分叉点上的中间代谢物,是所有芳香族氨基酸合成的共同前体.它可在双功能酶分支酸变位酶(CM)和预苯酸脱水酶(PDT)的催化下合成苯丙氨酸,在另一个双功能酶分支酸变位酶和预苯酸脱氢酶(PDH)的催化下合成酪氨酸.前者被称为P蛋白,后者被称为T蛋白.大肠杆菌P蛋白和T蛋白有着类似的结构,P蛋白由CMp、PDT和调节结构域3个独立结构域组成,其变构调节因子是苯丙氨酸.T蛋白只有CMt和PDH两个独立结构域组成,起变构调节作用的调节结构域与PDH密不可分,其变构调节因子是酪氨酸.为了研究P蛋白和T蛋白的调节结构域的变构调节作用,应用融合蛋白技术将P蛋白和T蛋白的调节结构域进行了互换.结果发现,互换了的调节结构域仍然具有变构调节作用,而且调节结构域的互换导致了变构调节因子的互换,说明调节结构域对酶活性的调节作用是非专一的,而其R结构域与调节因子的结合却是专一的.更多还原

【Abstract】 Chorismic acid is a mid-metabolite that plays a central role in the metablism process distributing in the bacterium, epiphyte and plants. It is a common precursor substance of the all aromatic amino acids that can turn into phenylalanine and tyrosine catalyzed by bi-functional enzyme chorismate mutase (CM)-prephenate dehydratase (PDT) and chorismate mutase-prephenate dehydrogenase (PDH) respectively. CM_p-PDT with its regulate domain R_p were called P-protein and CM_t-PDH with its regulate domain R_t were called T-protein. P-protein and T-protein from E. coli. have a similar structure, both of which contained three domains: CM_p, PDT, R_p in P-protein and CM_t, PDH, R_t in T-protein. P-protein and T-protein are regulated by their effectors phenylalanine and tyrosine respectively through binding to their R_p and R_t domains. R_p and R_t domains were switched between P-protein and T-protein by cloning of chimeric proteins. The results showed that regulatory effects were switched along the switch of R domains and the switch of the regulatory domains lead to the switch of effectors. It means that the combination of the regulatory domain and the effector is specific and the regulating of the regulatory domain to the enzyme activity is non-specific. This property of R domains may make them possible molecular elements in the study of molecular machines.更多还原