Infrared Spectroscopic Studies of Plant Photosynthesis

氧气光合作用发生在植物、蓝藻和藻类中，对维持地球上的生命是必不可少的。这种类型的光合作用需要两个光吸收反应中心的协同作用，这两个反应中心将光能转化为跨膜电荷分离。光系统II是这些反应中心之一，它催化水的氧化，产生分子氧和还原的质醌。光系统II在一个含锰的催化部位积累了产生氧气所需的四种氧化当量。催化中心的顺序氧化形式称为S态。光系统II由完整的跨膜亚基和不跨膜的外源亚基组成。已知这些非本征亚基的一个子集会影响光驱动的电子和质子转移事件。外源亚基被称为锰稳定蛋白，MSP可以防止PSII活性部位的锰损失，是最佳放氧率所必需的。在这个多学科的项目中，振动光谱学将被用来获得关于S状态周期期间发生的结构变化的详细信息。最终目标是确定在光合作用中氧-氧键是如何形成的。此外，振动光谱将被用来测试MSP可能影响水氧化的可能机制。最后，MSP与PSII反应中心结合时会改变构象或折叠的想法将通过X射线散射进行验证。这些实验将为复合膜蛋白的功能和组装提供新的信息。

Oxygenic photosynthesis occurs in plants, cyanobacteria, and algae and is essential in the maintenance of life on earth. This type of photosynthesis requires the concerted action of two light-absorbing reaction centers, which convert light energy into a transmembrane charge separation. One of these reaction centers, photosystem II catalyzes the oxidation of water and produces molecular oxygen and reduced plastoquinone. Photosystem II accumulates the four oxidizing equivalents necessary for oxygen production at a manganese-containing catalytic site. The sequentially oxidized forms of the catalytic site are called the S states. Photosystem II consists both of integral, membrane-spanning subunits and of extrinsic subunits, that do not span the membrane. A subset of these extrinsic subunits is known to influence light-driven electron and proton transfer events. The extrinsic subunit known as the manganese stabilizing protein, MSP, prevents loss of manganese from the PSII active site and is required for optimal rates of oxygen evolution. In this multidisciplinary project, vibrational spectroscopy will be used to obtain detailed information about structural changes occurring during the S state cycle. The ultimate goal is to determine how oxygen-oxygen bond formation occurs in photosynthetic oxygen evolution. In addition, vibrational spectroscopy will be employed to test a possible mechanism by which MSP may influence water oxidation. Finally, the idea that MSP changes conformation or folds when it binds to the PSII reaction center will be tested using X-ray scattering. These experiments will provide new information about the function and assembly of complex membrane proteins.