New Direction in Nuclear Magnetic Resonance of Copper and Zinc Ions in Biological Systems

金属及其离子是生命不可或缺的，因此生物系统中超过三分之一的蛋白质需要金属离子的存在才能发挥作用。几种过渡元素，包括铜（Cu）和锌（Zn），已被证明是人类所必需的，并以痕量（mg至g）存在于体内。铜和锌都是生命所必需的，但过量有毒，因此必须严格控制它们的体内平衡。为了了解Cu和Zn在体内的作用，了解这两种金属离子在其生物学背景下所采用的结合化学和配位环境是非常重要的。不幸的是，缺乏方便的物理和光谱性质来研究局部结构和动力学的金属网站迄今为止举行了详细了解Cu（I）和Zn（II）的生物化学。 核磁共振（NMR）光谱可能是探索溶液中分子结构和动力学的最强大的单一技术，因此，它从根本上促进了生物科学的进步。然而，在实践中，NMR对于元素周期表中的几种元素（包括Cu（I）和Zn（II））的灵敏度差，这主要是因为它们的NMR活性稳定同位素的低旋磁比和固有的小信噪比。此外，这两种核都是四极核（自旋> 1/2），导致共振线宽在kHz范围内或超出可检测范围，这使得它不适合许多前沿科学应用。因此，只有非常少的溶液相NMR研究Cu（I）和Zn（II）的生物系统中可以找到的文献。 该提案寻求资金，以调查铜（I）和锌（II）的金属结合位点直接在几个金属离子络合物和金属蛋白质的配位化学使用新建立的液相β-检测NMR（β-NMR）光谱。β-NMR使用放射性同位素而不是稳定同位素，并且它允许通过检测极化的放射性离子发射的β粒子来测量NMR信号。与传统的NMR光谱相比，它提供了1010的灵敏度增强，并且它可以应用于周期表中的许多元素，包括Cu（I）和Zn（II）。在过去的2-3年里，TRIUMF一直致力于在加拿大TRIUMF的ISAC-I设施中设计和实施液相β-NMR光谱仪。现在使用Mg-31完成了测试，明确确定β-NMR能够测量高质量的NMR共振，其分辨率优于传统的Mg-25 NMR，在2-3 L液体溶液中使用少至107个Mg离子，并且在不到一小时的时间内。鉴于最近的成就，我们现在已经准备好对不同的Cu（I）和Zn（II）结合生物系统进行开创性的β-NMR测量。

Metals and their ions are indispensable for life, and as such more than one third of all proteins in biological systems require the presence of metal ions to function. Several transition elements, including copper (Cu) and zinc (Zn), have been proven to be essential for humans, and occur in the body at trace amounts (mg to g). Cu and Zn are both necessary for life, but toxic in excess, and therefore their homeostasis has to be tightly controlled. In order to understand the role of Cu and Zn in the body, it is of profound importance to understand the binding chemistry and the coordination environment that these two metal ions adopt in their biological context. Unfortunately, the absence of convenient physical and spectroscopic properties to study the local structure and dynamics at the metal sites has so far held back a detailed understanding of Cu(I) and Zn(II) biochemistry. Nuclear magnetic resonance (NMR) spectroscopy is probably the most powerful single technique to explore the structure and dynamics of molecules in solution, and therefore, it contributes fundamentally to the advancement of biological sciences. In practice, however, NMR suffers from poor sensitivity for several elements across the periodic table, including both Cu(I) and Zn(II), mainly because of the low gyromagnetic ratio of their NMR-active stable isotopes and intrinsically small signal-to-noise ratio. Furthermore, both nuclei are quadrupolar (spin > 1/2), leading to resonance lines widths in the kHz range or beyond detectability, which makes it inadequate for many frontier scientific applications. As a result, only a very few solution-phase NMR studies on Cu(I) and Zn(II)-containing biological systems can be found in the literature. This proposal seeks funds to investigate the coordination chemistry of Cu(I) and Zn(II) metal-binding sites directly in several metal ion complexes and metalloproteins using the newly established liquid-phase beta-detected NMR (beta-NMR) spectroscopy. Beta-NMR employs radioisotopes rather than stable isotopes, and it allows for measuring NMR signals by detecting the beta particles emitted by polarized, radioactive ions. It offers 1010 enhancement in sensitivity as compared to conventional NMR spectroscopy, and it can be applied to many elements across the periodic table, including both Cu(I) and Zn(II). For the past 2-3 years, TRIUMF has been working on the design and implementation of the liquid-phase beta-NMR spectrometer at the ISAC-I facility at TRIUMF, Canada. Testing is now completed using Mg-31, unambiguously establishing that beta-NMR is capable of measuring high-quality NMR resonances with resolution better than conventional Mg-25 NMR, using as few as 107 Mg ions in 2-3 L of liquid solution, and within less than an hour. Given the recent accomplishments, we are now well poised to conduct pioneering beta-NMR measurements on different Cu(I) and Zn(II) binding biological systems.