The Many Facets of Coenzyme B12 Chemistry

有了这个奖项，化学部门的生命过程化学项目资助了威斯康星大学麦迪逊分校的托马斯·布鲁诺尔德博士研究维生素B12的化学成分。维生素是必需的营养物质，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是非凡的，因为它是生物中发现金属钴的少数分子之一。此外，维生素B12中的钴原子与碳原子结合，这种联系在生物学中非常罕见。这项研究运用了最先进的科学方法来了解这种不寻常的键是如何形成的，以及它是如何在三种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成分如何促进生物过程。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来增强的，这些实验室的例子来自于该奖项的研究结果。结合类角质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)类角质腺苷转移酶[ACATs]），底物的自由基重排（例如adoccl依赖性酶）和有机底物的脱卤（例如还原脱卤酶[rdaase]）。活性cob(I)alamin被认为是固醇o -酰基转移酶（也称为酰基coa胆固醇酰基转移酶或ACAT）酶机制的中间体。在酶转换过程中，这些物种的表征以前没有尝试过。该研究可能有助于详细了解ACATs如何完成Co(I)Cbl中间体的形成并控制其亲核性。就AdoCbl依赖性酶而言，人们普遍认为AdoCbl的Co-C键的均裂裂解产生5'-脱氧腺苷基自由基是其催化循环的第一步。然而，对于II类消去酶以独特的构象结合AdoCbl所显示的这一步骤的速率增强的起源知之甚少。该研究阐明了II类消去酶在响应底物结合时促进其AdoCbl辅因子的Co-C键均裂的机制。最后，b12依赖性rase最近引起了相当大的兴趣，因为它们对有机卤化物的生物修复至关重要。布鲁诺德教授和他的团队使用一系列光谱和计算方法来验证这种假设，即在这些酶的催化循环中形成了新型卤化类corcoroid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.