Kuroki R, Weaver L H, Matthews B W
Institute of Molecular Biology, Howard Hughes Medical Institute, University of Oregon, Eugene 97403, USA.
Nat Struct Biol. 1995 Nov;2(11):1007-11. doi: 10.1038/nsb1195-1007.
Here we show that the substitution Thr 26-->His in the active site of T4 lysozyme causes the product to change from the alpha- to the beta-anomer. This implies an alteration in the catalytic mechanism of the enzyme. From the change in product, together with inspection of relevant crystal structures, it is inferred that wild-type T4 lysozyme is an anomer-inverting enzyme with a single displacement mechanism in which water attacks from the alpha-side of the substrate. In contrast, the mutant T26H is an anomer-retaining enzyme with an apparently double displacement mechanism in which a water molecule attacks from the opposite side of the substrate. The results also show that the mechanism of wild-type T4 lysozyme differs from that of hen egg-white lysozyme even though both enzymes are presumed to have evolved from a common precursor.
我们在此表明，T4溶菌酶活性位点中的苏氨酸26被组氨酸取代，导致产物从α异头物转变为β异头物。这意味着该酶催化机制发生了改变。从产物的变化以及对相关晶体结构的检查可以推断，野生型T4溶菌酶是一种具有单取代机制的异头物转化酶，其中水从底物的α侧进攻。相比之下，突变体T26H是一种具有明显双取代机制的异头物保留酶，其中水分子从底物的相反侧进攻。结果还表明，野生型T4溶菌酶的机制与鸡蛋清溶菌酶不同，尽管这两种酶都被认为是从共同的前体进化而来的。
