Biophysical studies of the mechanisms of charge separation and recombination in bacterial photosynthetic reaction centers

光合作用是地球上最重要的太阳能转换过程。这种能量被用来驱动重要的细胞过程，如ATP或NADPH的合成，这些过程随后被用于将二氧化碳还原为碳水化合物。光合作用的初级反应发生在反应中心(Rc)，它是一种膜完整的色素蛋白。RC结构的一个显着特征是存在一个近似的局部C2对称轴，该对称轴由所谓的L分支和M分支中的光合作用小猪所定义。在这一背景下，一个重要的问题是蛋白质中的组织环境如何调节结合的假体基团的光谱和氧化还原性质，从而产生重要的功能结果，例如几乎完全沿着L分支的电子转移(ET)。本项目的目的是研究野生型细菌光合作用反应中心的电子传递过程的分子机制，以及几个缺乏杆状藻素辅助因子HL的突变体，从而获得高产的M-Side ET。对于这一目标，来自紫色细菌，如球形红杆菌或胶囊红杆菌的RCS是理想的选择。它们允许直接观察光诱导的电子转移过程，因为完全功能的RC可以通过生化分离，并且已经开发出通过定点突变来操纵RC结构的方案。通过拟议的研究，有望对电荷转移的单向性机制有更深入的了解。具体来说，像PHOTO-CIDNP和REDOR这样的固态核磁共振实验被认为是为了获得特定酪氨酸基的局部结构信息，这种结构信息被认为是调节反应能量并触发电荷分离的关键步骤。

Photosynthesis is the most important process for solar energy conversion on earth. The energy is used to drive important cellular processes such as synthesis of ATP or NADPH, which are subsequently used to reduce CO2 to carbohydrates. The primary reactions of photosynthesis occur in the reaction center (RC), which is a membrane-integral pigment-protein. A striking feature of the RC structure is the presence of an approximate local C2 axis of symmetry defined by the photosynthetic pigmets in the so-called L- and M-branches. An important question in this context is how the organized environment in proteins modulates the spectral and redox properties of bound prosthetic groups with important functional consequences such as electron transfer (ET) almost exclusively along the L-branch. The aim of this project is to investigate the molecular mechanisms of electron transfer processes in wild-type bacterial photosynthetic reaction centers and several mutants that lack the Bacteriopheophytin cofactor HL resulting in a high yield M-side ET. For this goal RCs from purple bacteria like Rhodobacter sphaeroides or Rhodobacter capsulatus are ideally suited. They allow a direct observation of the light-induced electron transfer processes since the fully functional RC can be isolated biochemically and protocols were developed to manipulate the RC structure by site-directed mutagenesis. From the proposed studies a deeper insight into the mechanism of the unidirectionality of charge-transfer is expected. In detail, solid-state NMR experiments like photo-CIDNP and REDOR are envisaged to obtain local structural information on a particular tyrosyl that is believed to modulate reaction energetics and triggers the key step of charge separation.