TIME-RESOLVED MAGNETIC CIRCULAR DICHROISM

时间分辨磁圆二色性

• 批准号: 6385684
• 负责人: DAVID S. KLIGER
• 金额: $ 24万
• 依托单位: UNIVERSITY OF CALIFORNIA SANTA CRUZ
• 依托单位国家: 美国
• 财政年份: 1987
• 资助国家: 美国
• 起止时间: 1987-07-01 至 2004-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6385684
• 关键词: allosteric site; chemical kinetics; circular magnetic dichroism; conformation; cytochrome c; cytochrome oxidase; electron transport; hemoglobin; hemoprotein structure; myoglobin; optical rotation; photolysis; protein folding; protein structure function; structural biology; time resolved data; ultraviolet radiation

This project will apply techniques for fast time-resolved magnetic circular dichroism (TRMCD) and magnetic optical rotatory dispersion (TRMORD) spectroscopies to the study of function and folding in heme proteins. The novel optical methods employed use quasi-null ellipsometry and polarimetry to study rapid kinetic processes (nanosecond to second time scales) in biomolecules that contain magneto-optically active chromophores such as heme and the aromatic amino acids. The overall program of the functional ligand-rebinding studies is to investigate protein relaxation after ligand photolysis with the goal of understanding how protein structure modulates the reactivity of the heme prosthetic group and elicits the variety of functions that heme proteins perform in oxidative metabolism. The proposed TRMCD studies of kinetic intermediates in the oxygen transport protein hemoglobin have the goal of better understanding the dynamics of the allosteric R yields T transition in this cooperative system. The TRMCD spectra of the near-UV tryptophan bands and the heme-based Soret and visible bands will be examined for MCD transients on the nanosecond and microsecond timescales that are characteristic of globin tertiary and quaternary structural changes after photolysis of the R-state carboxy adduct. Similarly, TRMCD/MORD studies of ligand photolysis in myoglobin will be directed toward resolving outstanding questions about the heme pocket dynamics underlying the function of this oxygen storage protein. Molecular oxygen is ultimately consumed in cells by redox reactions catalyzed at a copper-heme iron site in the enzyme cytochrome c oxidase. The TRMCD studies of ligand dynamics at the bimetallic site proposed here are ultimately addressed at a major puzzle in biophysics: How does cytochrome oxidase couple the energy released in this redox chemistry to the pumping of protons against a gradient? Finally, in the other major direction of investigation proposed, TRMCD/MORD techniques will be used to monitor ultrafast (submillisecond) events in the folding reactions of heme proteins. In particular, this work will look for direct spectrokinetic evidence for the type of biased diffusional dynamics thought to characterize the earliest events in the folding of protein chains in the new, energy landscape point of view.

本计画将应用快速时间分辨磁性圆二色性（TRMCD）与磁性旋光色散（TRMORD）光谱技术，研究血红素蛋白质的功能与折叠。 新的光学方法采用准零椭圆偏振法和旋光法研究快速动力学过程（纳秒到秒的时间尺度）在生物分子，含有磁光活性生色团，如血红素和芳香族氨基酸。 功能性配体再结合研究的总体方案是研究配体光解后的蛋白质弛豫，目的是了解蛋白质结构如何调节血红素辅基的反应性，以及血红素蛋白在氧化代谢中执行的各种功能。 建议的TRMCD研究的动力学中间体的氧转运蛋白血红蛋白的目标是更好地了解在这个合作系统中的变构R产生T转换的动力学。 近紫外色氨酸谱带和血红素的Soret和可见光谱带的TRMCD光谱将检查MCD瞬变的纳秒和微秒的时间尺度，是球蛋白的三级和四级结构变化的特征后，光解的R-状态羧基加合物。同样，TRMCD/MORD研究肌红蛋白中的配体光解将直接解决悬而未决的问题血红素口袋动力学的功能，这种储氧蛋白。分子氧最终在细胞中通过在酶细胞色素c氧化酶中的铜-血红素铁位点催化的氧化还原反应消耗。 TRMCD研究的配体动力学在这里提出的dielectric网站最终解决在生物物理学中的一个主要难题：细胞色素氧化酶如何耦合的能量释放在这个氧化还原化学泵的质子对梯度？ 最后，在提出的其他主要研究方向，TRMCD/MORD技术将被用来监测超快（亚毫秒）事件的血红素蛋白质的折叠反应。 特别是，这项工作将寻找直接spectrokinetic证据的类型有偏见的扩散动力学认为最早的事件在新的，能源景观的角度来看，蛋白质链折叠的特点。