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

• Applicant: Dr. Miguel Saggu
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2010 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 182537781

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.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Dr. Steven G. Boxer