Structure, Function and Biogenesis of Cyanobacterial Photosystem I

在蓝藻和植物中，光系统I （PS 1）反应中心（RC）是一种膜结合的多亚基氧化还原酶，它催化从类囊体腔侧还原的质体青素（或经常是细胞色素C6）到氧化的铁氧还蛋白（或黄氧还蛋白）的光驱动电子转移。本研究计划的长期目标是了解这种复杂酶的生物起源，以及结构和机制细节，使其能够催化上述反应，量子产率接近1.0，热力学效率非常高（~45%）。利用在本资助期内获得的知识，将利用位点定向和一般诱变、蛋白质过剩生产、生化分辨率和重构、化学救援和修饰、光学动力学光谱、X和q波段EPR光谱、瞬态EPR光谱、脉冲EPR光谱、核磁共振光谱和质谱等强大的方法来生产和分析具有新性质的PS I反应中心。研究的长期目标是：(1)RubA和Ycf4在PS I生物发生中的作用；(2)醌修饰的PS I配合物的电子传递动力学；(3) 2-甲基在叶绿醌功能中的作用，完成了叶绿醌生物合成途径的建立；(4)质体醌生物合成途径的建立及不能合成质体醌的突变体的性质；(5) PsaC的结构特性对FA和F13的磁性和氧化还原特性的影响。本研究的成功完成将为研究膜结合电子传递蛋白的生物发生提供重要的新信息；将严格检验当前生物电子传递过程的理论描述；并将为蓝藻中叶绿醌和塑性醌的生物合成途径提供重要的新信息。地球上的所有生命最终都依赖于光能捕获，并通过光合作用将能量转化为生物质。蓝藻的光合作用不仅在全球碳和氮的循环中起着核心作用，而且在包括海洋在内的许多生态系统中，这些生物是生物量的主要主要生产者。蓝藻是光自养的原核生物，其光合装置与高等植物叶绿体中的光合装置非常相似。然而，由于蓝藻可以像其他原核生物一样进行实验操作，并且由于相对复杂的遗传方法可以用于这些生物，因此蓝藻为理解含氧光合作用的模型系统提供了独特的机会。更好地了解这些过程可以改善农业上重要的农作物，生产重要的生物材料和生物传感器的方法，以及温室气体改善方法的可能方法。该项目还为微生物生理学、分子生物学、生物化学和生物物理学等领域的学生和博士后提供了良好的多学科培训机会。

0077586BryantIn cyanobacteria and plants, the Photosystem I (PS 1) reaction center (RC) is a membrane-bound, multisubunit oxidoreductase that catalyzes the light-driven transfer of electrons from reduced plastocyanin (or frequently cytochrome C6) on the lumenal side of the thylakoid to oxidized ferredoxin (or flavodoxin). The long-term goal of this research program is to understand the biogenesis of this complex enzyme, as well as the structural and mechanistic details that allow it to catalyze the above-mentioned reaction with a quantum yield approaching 1.0 and a very high thermodynamic efficiency (~45%). Taking advantage of knowledge gained during the present funding period, the powerful methods of site-directed and general mutagenesis, protein overproduction, biochemical resolution and reconstitution, chemical rescue and modification, optical kinetic spectroscopy, X- and Q-band EPR spectroscopy, transient EPR spectroscopy, pulsed EPR spectroscopy, NMR spectroscopy, and mass spectrometry will be employed to produce and to analyze PS I reaction centers with novel properties. The following (long-term) goals will be studied: (1) the roles of RubA and Ycf4 in PS I biogenesis; (2) electron transport kinetics in PS I complexes with modified quinone contents; (3) the role of the 2-methyl group in phylloquinone function and complete establishment of the biosynthetic pathway for phylloquinone biosynthesis; (4) establishment of the biosynthetic pathway for plastoquinone and the properties of mutants unable to synthesize plastoquinone; and (5) an examination of structural properties of PsaC that influence the magnetic and redox properties Of FA and F13. The successful completion of the proposed research program would contribute significant new information concerning the biogenesis of membrane- bound, electron transport proteins; would critically test current theoretical descriptions of biological electron transport processes; and would contribute important new information concerning the biosynthetic pathways for phylloquinone and plastoquinone in cyanobacteria.All life on Earth is ultimately dependent upon light-energy capture and energy conversion to biomass through photosynthesis. Cyanobacterial photosynthesis is not only centrally important in the global cycling of carbon and nitrogen, but these organisms are the major primary producers of biomass in many ecosystems, including the oceans. Cyanobacteria are photoautotrophic prokaryotes whose photosynthetic apparatus closely resembles that found in the chloroplasts of higher plants. However, because cyanobacteria can be experimentally manipulated like other prokaryotes, and because relatively sophisticated genetic methods can be employed with these organisms, cyanobacteria provide unique opportunities as model systems for understanding oxygenic photosynthesis. A better understanding of these processes can lead to improvements in agriculturally important crop plants, to methods for the production of important biomaterials and biosensors, and to possible methods for greenhouse gas amelioration methods. This project also provides outstanding opportunities for multidisciplinary training of students and postdoctoral fellows in areas including microbial physiology, molecular biology, biochemistry, and biophysics.