The Influence of Cysteinate Protonation in Nickel Containing Metalloenzymes

项目摘要。半胱氨酸连接的镍金属酶存在于多种病原菌中。 其中一些含镍的金属酶，如在 幽门螺杆菌是在导致人类疾病的微生物中发现的。至少两个含镍的 金属酶，含镍超氧化物歧化酶(NiSOD)和[NiFe]H_2酶，具有协调的 质子化半胱氨酸残基(Ni-S(H+)-半胱氨酸)。我们怀疑Ni-S(H+)-半胱氨酸键参与了 酶的作用机制，也调节这些金属酶的电子结构和反应活性。 我们的研究将利用基于功能金属酶的NiSOD模拟物和小分子 模拟[NiFe]H_2酶。我的团队已经准备好复制基于金属肽的镍超氧化物歧化酶的模拟 金属酶的结构和物理性质。这些金属多肽还具有催化活性， 影响O2-歧化反应的速率常数接近于金属酶中观察到的速率常数。近期 我的团队的研究表明，这些模拟分子通过一种独特的质子促进O2-还原为H2O2 Ni-S(H+)-半胱氨酸部分与O-的耦合电子转移反应。我们将通过以下方式来探讨这种反应 2. 制备将改变PCET反应的基本性质的这些金属多肽的衍生物。这 将深入了解由这些部分促进的PCET反应的一般范围。此外，我们还将 制备更准确地复制酶反应的金属多肽NiSOD模拟物 机制。初步的研究表明，植物体内O2-还原的机制可能是 金属多肽不同于NiSOD本身。通过生产复制酶反应的模拟物，我们将 更好地了解NiSOD本身对O2-歧化的影响机制。此外，我们还将 研究了Ni-S(H+)-半胱氨酸部分对[NiFe]H_2酶模型化合物的影响。我们建议， 配位半胱氨酸配体的质子化显著改变了镍中心的电子结构 在[NiFe]-H_2酶中，特别是在fi中，它减少了机械上重要的Ni(III)-H中间体的水合度 偏置[NiFe]H_2酶以执行氢氧化化学。这一假设也将在这一倡议下进行探讨。 这项研究涵盖了生物无机化学中使用的各种工具。就像我们的许多研究是合成的一样， 生物化学、光谱学、机械学和计算方面的研究将用于理解 金属多肽和小分子模拟的方方面面。金属酶模拟物在我国的应用 调查尤其值得注意；很少有研究深入了解物种fic 以金属多肽为基础的金属酶模拟物揭示了生化过程。因此 该项目的完成不仅将揭示具有重要生物学意义的镍-S(H+)-半胱氨酸的有趣方面 部分，但也将推动金属多肽类金属酶研究的极限 模仿。

Project Summary. Cysteinate ligated nickel metalloenzymes are found in a number of pathogenic bacteria. Some of these nickel containing metalloenzymes, such as nickel-iron hydrogenase ([NiFe]H2ase) found in Helicobacter pylori, are found in microbes responsible for human diseases. At least two nickel containing metalloenzymes, nickel containing superoxide dismutase (NiSOD) and [NiFe]H2ase, possess a coordinated protonated cysteinate residue (Ni-S(H+)-Cys). We suspect that the Ni-S(H+)-Cys bond is involved in the enzymatic mechanism and also modulates the electronic structure and reactivity of these metalloenzymes. Our research will take advantage of functional metalloenzyme based mimics of NiSOD and small molecule mimics of [NiFe]H2ase. Metallopeptide based mimics of NiSOD that my group has prepared to date reproduce the structure and physical properties of the metalloenzyme. These metallopeptides are also catalytically active, effecting O2– disproportionation with rate constants approaching those observed in the metalloenzyme. Recent work by my group has demonstrated that these mimics facilitate O2– reduction to H2O2 via a unique proton coupled electron transfer (PCET) reaction from a Ni-S(H+)-Cys moiety to O –. We will probe this reaction by 2 preparing derivatives of these metallopeptides that will alter the fundamental nature of the PCET reaction. This will yield insight into the general scope of PCET reactions facilitated by such moieties. In addition, we will prepare metallopeptide based NiSOD mimics that more accurately replicate the enzymatic reaction mechanism. Preliminary work demonstrates that the mechanism of O2– reduction effected by the metallopeptide is distinct from NiSOD itself. By producing mimics that reproduce enzymatic reactivity we will gain a better understanding of the mechanism of O2– disproportionation effected by NiSOD itself. Also, we will investigate the influence of the Ni-S(H+)-Cys moiety on [NiFe]H2ase model compounds. We propose that the protonation of the coordinated cysteinate ligand is dramatically altering the electronic structure of the Ni-center in [NiFe]-H2ase; specifically it is reducing the hydricity of the mechanistically important Ni(III)-H intermediate biasing [NiFe]H2ase to perform H2 oxidation chemistry. This supposition will also be probed under this initiative. This research runs the gamut of tools utilized in bioinorganic chemistry. As with many of our studies synthetic, biochemical, spectroscopic, mechanistic, and computational studies will be brought to bear on understanding all aspects of the metallopeptides and small molecule mimics. The use of metalloenzyme mimics in our investigations is especially noteworthy; few studies have been performed where insight into specific biochemical processes are revealed through metallopeptide based metalloenzyme mimics. Therefore completion of this project will not only reveal interesting aspects of biologically important Ni-S(H+)-Cys moieties, but will also push the limits of investigations concerning metallopeptide based metalloenzyme mimics.