Infrared Spectroscopic Studies of Plant Photosynthesis

含氧光合作用发生在植物、蓝藻和藻类中，对维持地球上的生命至关重要。这种类型的光合作用需要两个吸收光的反应中心协同作用，将光能转化为跨膜电荷分离。其中一个反应中心，光系统II催化水的氧化并产生分子氧和还原性质体醌。光系统II在含锰的催化位点积累了四种氧化等价物，这些氧化等价物是产氧所必需的。催化位点的顺序氧化形式称为S态。光系统II既有跨膜的整体亚基，也有不跨膜的外在亚基。已知这些外在亚基的一个子集会影响光驱动的电子和质子转移事件。外部亚基称为锰稳定蛋白（MSP），可防止PSII活性位点的锰损失，并且是最佳出氧速率所必需的。在这个多学科项目中，振动光谱学将用于获得S态周期中发生的结构变化的详细信息。最终的目标是确定在光合作用的氧气演化过程中氧-氧键的形成是如何发生的。此外，振动光谱学将用于测试MSP可能影响水氧化的可能机制。最后，MSP在与PSII反应中心结合时改变构象或折叠的想法将使用x射线散射进行测试。这些实验将为复杂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.