GLOBAL MAPPING OF XAS DATA STRUCTURE OF ACTIVE SITE OF COBALAMIN ENZYMES

钴胺素的两种晶体结构 依赖酶，27 kDa片段的 甲基钴胺素依赖酶，蛋氨酸合酶， 大肠杆菌[C. L. Drennan等人，Science，266，1669（1994）]和 的5- 脱氧腺苷钴胺素依赖酶甲基丙二酰辅酶 从谢氏丙酸杆菌（Propionibacterium shermanii）[F. Mancia等人 结构，4，339（1996）]，显示出惊人的相似性，尽管 反应机制的差异。 特别是 5，6-二甲基苯并咪唑基团被分离并被取代， 酶的组氨酸基团。 我们分析了扩展X射线 吸收精细结构（EXAFS）光谱数据， 5- 脱氧腺苷钴胺素和水钴胺素， 甲基丙二酰-辅酶A在无底物的情况下。 的 用一套称为AUTOFIT 1.0的程序进行分析 [Chance等人，Biochemistry，1996，35，9014]，其允许 EXAFS数据的拟合优度与 基于从头算EXAFS代码FEFF的不同网格模拟 6.01. X射线边缘数据表明， 酶结合的金属离子的电荷5- 脱氧腺苷钴胺素 与相应的游离钴胺素和EXAFS结果相比， 在赤道地区略有下降，在赤道地区没有明显变化。 Co-C键长

The two available crystallographic structures of cobalamin dependent enzymes, the 27 kDa fragment of the methylcobalamin-dependent enzyme, methionine synthase, from Escherichia coli [C. L. Drennan et al. Science, 266, 1669 (1994)] and the 5-deoxyadenosylcobalamin-dependent enzyme methylmalonyl-coenzyme A mutase from Propionibacterium shermanii [F. Mancia et al. Structure, 4, 339 (1996)], show striking similarities despite the differences in reaction mechanism. In particular, the 5,6-dimethylbenzimidazole group is detached and replaced by a histidine group of the enzyme. We have analyzed Extended X-ray Absorption Fine Structure (EXAFS) spectroscopic data for both 5-deoxyadenosylcobalamin and aquocobalamin bound to methylmalonyl-coenzyme A mutase in the absence of substrate. The analysis is conducted with a suite of programs called AUTOFIT 1.0 [Chance et al., Biochemistry, 1996, 35, 9014], which allows an evenhanded comparison of the goodness-of-fit of the EXAFS data to a varied grid of simulations based on the ab initio EXAFS code FEFF 6.01. The x-ray edge data indicate an increase in effective nuclear charge of the metal ion of the enzyme bound 5-deoxyadeonsylcobalamin compared to the corresponding free cobalamin and the EXAFS results show small decreases in equatorial and no significant change in the Co-C bond length.