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许多病原菌中。 这些含镍金属酶中的一些，如在大肠杆菌中发现的镍铁氢化酶（[NiFe] H2酶）， 幽门螺杆菌是在微生物中发现的导致人类疾病的细菌。至少两个含镍 金属酶，含镍超氧化物歧化酶（NiSOD）和[NiFe] H2酶，具有协调的 质子化半胱氨酸残基（Ni-S（H+）-Cys）。我们怀疑Ni-S（H+）-Cys键参与了 酶的机制，也调节这些金属酶的电子结构和反应性。 我们的研究将利用功能性金属酶为基础的模拟NiSOD和小分子 [NiFe] H2酶的模拟物。我的小组迄今为止准备的基于金属肽的NiSOD模拟物， 金属酶的结构和物理性质。这些金属肽也具有催化活性， 以接近在金属酶中观察到的速率常数实现O2-反硝化。最近 我的小组的工作已经证明，这些模拟物通过一个独特的质子促进O2还原为H2 O2 从Ni-S（H+）-Cys部分到O -的偶联电子转移（PCET）反应。我们将通过以下方式来探测该反应： 2 制备将改变PCET反应的基本性质的这些金属肽的衍生物。这 将产生洞察PCET反应的一般范围促进了这样的部分。此外，我们将 制备基于金属肽的NiSOD模拟物，其更准确地复制酶促反应 机制初步研究表明，O_2 ~-还原的机理是由 金属肽不同于NiSOD本身。通过生产复制酶反应性的模拟物， 进一步了解了NiSOD本身对O2-还原的影响机制。我们亦会 研究了Ni-S（H+）-Cys结构对[NiFe] H2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Ni中心的电子结构 在[NiFe]-H2酶中;特别是它降低了机械上重要的Ni（III）-H中间体的水合性 偏置[NiFe] H2酶以进行H2氧化化学反应。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。与我们的许多合成研究一样， 生物化学、光谱学、机械学和计算研究将对理解产生影响 金属肽和小分子模拟物的所有方面。金属酶模拟物在我们的 研究尤其值得注意;很少有研究深入了解特定的 通过基于金属肽的金属酶模拟物揭示了生物化学过程。因此 该项目的完成不仅将揭示生物学重要的Ni-S（H+）-Cys的有趣方面， 部分，但也将推动有关金属肽的金属酶的研究限制 模仿者

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.