The Many Facets of Coenzyme B12 Chemistry

有了这个奖项，化学部的生命过程化学项目资助威斯康星大学麦迪逊分校的托马斯布鲁诺博士研究维生素B12的化学。 维生素是必需的营养素，因为它们有助于生命系统中发生的各种化学变化。 维生素B12是一种特殊的维生素，因为它是生物学中发现的少数几种含有金属钴的分子之一。此外，钴原子与维生素B12中的碳原子键合，这种连接在生物学中非常罕见。 这项研究采用了最先进的科学方法来了解这种不寻常的联系是如何形成的，以及它是如何在三个特定的生物系统中使用的。 参与该项目的研究生和本科生将深入了解钴的特殊化学如何有助于生物过程。 这项工作的更广泛的影响是通过一个开放的实验室研讨会和一个本科生无机实验室与来自该奖项的研究结果的例子得到加强。结合类咕啉辅因子的酶催化许多独特的化学转化，包括钴（Co）-碳（C）键的形成（例如ATP：Co（I）类蛋白腺苷转移酶[ACATs]），底物的基于自由基的重排（例如，H2 O2依赖性酶）和有机底物的脱卤（例如，还原性脱卤酶[RDases]）。 反应性辅酶（I）丙氨酸被假定为固醇O-酰基转移酶（也称为酰基辅酶A胆固醇酰基转移酶或ACAT）酶机制中的中间体。这些物种在酶周转过程中的表征以前没有尝试过。该研究可能导致详细了解ACATs如何完成Co（I）Cbl中间体的形成并控制其亲核性。在β-Cbl依赖性酶的情况下，广泛接受的是β-Cbl的Co-C键的均裂断裂以产生基于5 '-脱氧腺苷基的自由基代表了其催化循环的第一步。然而，鲜为人知的是，这一步显示的II类消除酶，它结合在一个独特的构象中的ESTCBL的速率增强的起源。该研究阐明了II类消除酶用于促进它们的CycloCbl辅因子的Co-C键的均裂以响应底物结合的机制。最后，B12依赖的RDases最近吸引了相当大的兴趣，因为它们是有机卤化物的生物修复的关键。Brunold教授和他的研究小组使用一系列光谱和计算方法来检验这一假设，即在这些酶的催化循环中形成了新的卤代类可啉中间体。

With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Thomas Brunold from the University of Wisconsin-Madison to study the chemistry of vitamin B12. Vitamins are necessary nutrients because they assist in various chemical changes that take place in living systems. Vitamin B12 is extraordinary because it is one of the few molecules in biology where the metal cobalt is found. In addition, the cobalt atom is bonded to carbon in vitamin B12, a connection that is very rarely seen in biology. The research applies state-of-the-art scientific methods to understand how this unusual bond is made, and how it is used in three specific biological systems. Graduate and undergraduate students involved in this project gain a thorough understanding of how the special chemistry of cobalt contributes to biological processes. The broader impacts of this work are enhanced by an open-house laboratory workshop and an undergraduate inorganic laboratory with examples derived from the research resulting from this award.Enzymes that bind corrinoid cofactors catalyze a number of unique chemical transformations, including cobalt (Co)- carbon (C) bond formation (e.g. ATP:Co(I)rrinoid adenosyltransferases [ACATs]), radical-based rearrangement of substrates (e.g. AdoCbl-dependent enzymes), and dehalogenation of organic substrates (e.g. reductive dehalogenases [RDases]). Reactive cob(I)alamin species are postulated as intermediates in the sterol O-acyltransferase (also called Acyl-CoA cholesterol acyltransferase or ACAT) enzyme mechanisms. A characterization of these species during enzyme turnover has not previously been attempted. The research may lead to a detailed understanding of how ACATs accomplish the formation of Co(I)Cbl intermediates and control their nucleophilicity. In the case of AdoCbl-dependent enzymes, it is widely accepted that the homolytic cleavage of the Co-C bond of AdoCbl to generate a 5'-deoxyadenosyl-based radical represents the first step in their catalytic cycles. Yet, little is known about the origin of the rate enhancement for this step displayed by Class II eliminases, which bind AdoCbl in a unique conformation. The research elucidates the mechanism used by Class II eliminases to promote homolysis of the Co-C bond of their AdoCbl cofactors in response to substrate binding. Lastly, the B12-dependent RDases have recently attracted considerable interest because they are critical for the bioremediation of organohalides. Professor Brunold and his group use a range of spectroscopic and computational methods to test the hypothesis that novel halogenated corrinoid intermediates are formed in the catalytic cycles of these enzymes.