Structure, Function and Biogenesis of Cyanobacterial Photosystem I

在蓝细菌和植物中，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，其催化电子从类囊体内腔侧的还原质体蓝蛋白（或通常为细胞色素C6）到氧化铁氧还蛋白（或黄素氧还蛋白）的光驱动转移。该研究计划的长期目标是了解这种复杂酶的生物起源，以及使其能够以接近1.0的量子产率和非常高的热力学效率（~45%）催化上述反应的结构和机理细节。利用在目前资助期间获得的知识，定点和一般诱变、蛋白质过量生产、生化解析和重建、化学拯救和修饰、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、NMR光谱、质谱法将用于产生和分析具有新性质的PS I反应中心。以下（长期）研究目标是：（1）RubA和Ycf 4在PS I生物合成中的作用，（2）具有修饰醌含量的PS I复合物中的电子传递动力学，（3）2-甲基在叶绿醌功能中的作用，以及叶绿醌生物合成途径的完整建立;（4）建立质体醌的生物合成途径和不能合成质体醌的突变体的性质;和（5）检查影响FA和F13的磁性和氧化还原性质的PsaC的结构性质。成功完成拟议的研究计划将有助于重要的新信息有关的生物起源的膜结合，电子传递蛋白质，将严格测试目前的理论描述的生物电子传递过程;并将为蓝藻中叶绿醌和质体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-通过光合作用捕获能量并将能量转化为生物质。蓝藻光合作用不仅在全球碳和氮循环中至关重要，而且这些生物体是包括海洋在内的许多生态系统中生物量的主要初级生产者。蓝细菌是一种光合自养的原核生物，其光合机构与高等植物的叶绿体非常相似。然而，因为蓝细菌可以像其他原核生物一样进行实验操作，并且因为相对复杂的遗传方法可以用于这些生物体，所以蓝细菌提供了独特的机会作为理解产氧光合作用的模型系统。对这些过程的更好理解可以导致农业上重要的作物植物的改进，重要的生物材料和生物传感器的生产方法，以及温室气体改良方法的可能方法。该项目还为学生和博士后研究员在微生物生理学，分子生物学，生物化学和生物物理学等领域的多学科培训提供了绝佳的机会。

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.