EXAFS SPECTROSCOPIC STUDIES OF THE NIFE 'C-CLUSTER' IN CARBON MONOXIDE DEHYDROGE

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。细菌红色葡萄球菌(R.rubrum，RR)和产氢葡萄球菌(C.H.genformans，CH)含有一种镍一氧化碳脱氢酶(CodH)，使它们能够以CO为唯一碳源生长。NiCODH的活性中心是所谓的“C-簇”，这是一个新的催化CO氧化为CO2的Ni-Fe-S中心。最近的X射线结晶学表明，C-簇包含一个配位到FeS4单元的Ni，桥接到外部的Fe位置。这令人惊讶，因为之前的EXAFS分析排除了对称的NiFeS4单元。然而，不同的C-簇晶体结构表现出显著的差异，并且它们也显示出在给定晶体内的簇异质性的证据。我们最近的EXAFS数据显示了还原和/或CO结合上的团簇重新排列的证据。这意味着，团簇结构动态地重新排列，或者作为“激活”过程的一部分，或者作为其催化机制的一部分。我们建议用EXAFS来研究RR和CH CODH的C-簇位点的结构变化。这是对C星团的全面光谱研究的一部分。我们计划研究已经被还原稳定、CO结合和抑制的酶。我们有可用的RR CODH变体，其中活性位点残基已被修改，其中外部Fe被删除。我们还有钴-钴和锌-钴，其中镍被另一种过渡金属取代。我们相信，使用EPR、FT-IR和共振拉曼光谱作为对照，我们可以制备用于EXAFS分析的均匀的C-团簇样品。这应该使我们能够对C-簇的结构动力学进行参数化，并从那里了解支持簇化学的基础，并最终了解这个具有生物重要性的酶系统的催化循环。此外，所发现的新的生物无机化学很可能导致新型催化剂的开发。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The bacteria R. rubrum (Rr) and C. hydrogenoformans (Ch) contain a Ni carbon monoxide dehydrogenase (CODH) that enables them to grow on CO as their sole carbon source. The active site of Ni CODH is the so-called 'C-cluster' a novel Ni-Fe-S center that catalyzes the oxidation of CO to CO2. Recent X-ray crystallography has shown the 'C-cluster' to comprise a Ni coordinated to a FeS4 unit, bridged to an external Fe site. This was a surprise, as prior EXAFS analysis had excluded a symmetric NiFeS4 unit. However, the various 'C-cluster' crystal structures show significant differences with each other, and, they also show evidence of cluster heterogeneity within a given crystal. We have recent EXAFS data that shows evidence of cluster re-arrangement on reduction and/or CO binding. The implication is that the cluster structure dynamically rearranges, either as part of an "activation" process, or as part of its catalytic mechanism. We propose to use EXAFS to investigate the structural changes of the 'C-cluster' sites for Rr and Ch CODH. This is part of a comprehensive spectroscopic study on the C-cluster. We plan to study enzyme that has been: reductively poised; CO-bound and inhibited. We have available variants of Rr CODH where active site residues have been modified, one where the external Fe is deleted. We also have Co-CODH and Zn-CODH, where the Ni has been replaced by another transition metal. We are confident that, using other spectroscopies such as EPR, FT-IR and resonance Raman as controls, we can prepare homogeneous C-cluster samples for EXAFS analysis. This should enable us to parameterize the C-cluster structural dynamics and from there understand the underpinning cluster chemistry and eventually the catalytic cycle of this biologically important enzyme system. In addition, the novel bioinorganic chemistry uncovered could well lead to the development of novel catalysts.