Barak Dov, Ordentlich Arie, Kaplan Dana, Kronman Chanoch, Velan Baruch, Shafferman Avigdor
Department of Organic Chemistry, Israel Institute for Biological Research, P.O. Box 19, Ness-Ziona 74100, Israel.
Chem Biol Interact. 2005 Dec 15;157-158:219-26. doi: 10.1016/j.cbi.2005.10.030. Epub 2005 Nov 11.
Determination of the 3D-structure of acetylcholinesterase (AChE) of Torpedo californica over a decade ago, and more recently that of human enzyme together with extensive targeted mutagenesis of the mammalian AChEs led to a fine mapping of the multiple functional domains within the active center of the enzyme. Many of the contributions of this active center architecture to accommodation of noncovalent ligands could be deduced from the X-ray structures of the corresponding HuAChE complexes. Yet, Michaelis complexes leading to transient covalent adducts are not amenable to structural analysis. Since the rates of formation of the covalent adducts depend predominantly on the stabilities of the corresponding Michaelis complexes, it is essential to characterize the specific interactions contributing to stabilization of these complexes. Functional analysis of interactions with HuAChE enzymes allows for such characterization for carbamates, like pyridostigmine or rivastigmine, much in the same way as that for the noncovalent therapeutic ligands nivalin or aricept. In fact, the observed differences between the affinities toward carbamates and the noncovalent ligands seem to result from specific structural characteristics of the inhibitors rather than from the decomposition path of the particular complex. Replacements at the cation binding site (Trp86), hydrogen bond network (Glu202, Tyr133, Glu450), and hydrophobic pocket result in similar effects for the covalent as well as for the noncovalent inhibitors. Also, while the effects of perturbing the aromatic trapping of the catalytic His447 for pyridostigmine and nivalin were analogous to those for the substrate, the corresponding effects for rivastigmine and aricept were quite different. Thus, elucidation of the functional architecture of the HuAChE active center is bound to be of considerable utility in the current effort to design novel covalent AChE inhibitors as therapeutics for Alzheimer's disease (AD).
十多年前测定了加州电鳐乙酰胆碱酯酶（AChE）的三维结构，最近又测定了人类该酶的三维结构，同时对哺乳动物AChEs进行了广泛的定向诱变，从而对该酶活性中心内的多个功能域进行了精细定位。该活性中心结构对非共价配体容纳的许多贡献可从相应的人AChE复合物的X射线结构中推导出来。然而，导致瞬时共价加合物的米氏复合物不适用于结构分析。由于共价加合物的形成速率主要取决于相应米氏复合物的稳定性，因此必须表征有助于稳定这些复合物的特定相互作用。对与人AChE酶相互作用的功能分析能够对氨基甲酸酯类药物进行这种表征，如吡啶斯的明或利伐斯的明，其方式与非共价治疗性配体尼伐林或安理申非常相似。事实上，观察到的对氨基甲酸酯类药物和非共价配体亲和力的差异似乎是由抑制剂的特定结构特征而非特定复合物的分解途径导致的。阳离子结合位点（Trp86）、氢键网络（Glu202、Tyr133、Glu450）和疏水口袋的取代对共价和非共价抑制剂产生类似的影响。此外，虽然干扰催化性His447对吡啶斯的明和尼伐林的芳香捕获作用与对底物的作用类似，但对利伐斯的明和安理申的相应作用却大不相同。因此，阐明人AChE活性中心的功能结构对于当前设计新型共价AChE抑制剂作为阿尔茨海默病（AD）治疗药物的努力必然具有相当大的实用价值。
