Unique Properties of the Chlorophyll in the Cytochrome b6f Complex

这项研究的目的，由生物科学理事会分子和细胞生物科学部的分子生物物理学和数学和物理科学理事会物理学部的生物物理学计划共同支持的是了解叶绿素（Chl）对单线态氧形成的新的独特保护机制a在细胞色素b6 f复合物的产氧光合作用，并解决不寻常的作用，叶绿素a在这个复杂的。最近的X射线结构表明，β-胡萝卜素是太远的Chl a的保护蛋白质从单线态氧形成的传统的直接三重态-三重态能量转移机制。提出了Chl a通过两种非常规机制受到保护：（i）Chl单重激发态电子转移交换猝灭机制和（ii）Chl a到β-胡萝卜素的长程氧介导的三重态能量流。为了检验这些假设，将在氧控制条件下使用位点特异性诱变和时间分辨光谱法进行一系列实验。此外，几种基于结构的数值方法将被应用于模拟观测数据。这些研究将导致对色素激发态猝灭机制、活性氧猝灭和转移机制、通过膜内蛋白质复合物的氧转移途径以及细胞色素b6 f复合物的结构的重大新见解。作为涉及生物学和物理学系的跨学科项目，该项目为物理和生物学生提供了一个独特的经验，将高科技激光光谱学和量子力学建模与定点诱变相结合，并将帮助他们在物理和生物科学方面打下坚实的基础。这项研究的结果还将用于各种“推广”方案和课程，旨在提高大学和高中学生对现代科学跨学科性质的认识。

The objective of this research, jointly supported by Molecular Biophysics in the Division of Molecular and Cellular Biosciences in the Directorate for Biological Sciences and the Biological Physics Program in the Division of Physics in the Mathematical and Physical Sciences Directorate is to understand the new and unique mechanisms of protection against singlet oxygen formation by the chlorophyll (Chl) a in the cytochrome b6f complex of oxygenic photosynthesis and to address the unusual role the Chl a plays in this complex. The recent X-ray structures indicate that the beta-carotene is too far from the Chl a to protect the protein from singlet oxygen formation by conventional direct triplet-triplet energy transfer mechanism. It is proposed that the Chl a is protected through two unconventional mechanisms: (i) Chl singlet excited state quenching by electron transfer exchange mechanism and (ii) long-range oxygen mediated triplet energy flow from the Chl a to the beta-carotene. To test these hypotheses a series of experiments will be performed using site-specific mutagenesis and time-resolved optical spectroscopy in oxygen controlled conditions. In addition, several structure-based numerical methods will be applied to model the observed data. These studies will lead to major new insights on the mechanism of quenching of pigment excited states, the mechanism of quenching and transfer of reactive oxygen species, pathways of oxygen transfer through intramembrane protein complexes, and the structure of the cytochrome b6f complex.Being an interdisciplinary project involving Biology and Physics departments, this project offers physics and biology students a unique experience that combines high-tech laser spectroscopy and quantum mechanical modeling with site directed mutagenesis, and will help them to develop a strong foundation in physics and biosciences. The results of this research will be also used in various "outreach" programs and courses designed to increase the awareness of university and high school students of the interdisciplinary nature of modern science.