9723001 Chitnis 1. Technical Photosystem I, the light-driven plastocyanin-ferredoxin oxidoreductase, is a heteromultimeric pigment-protein complex in the photosynthetic membranes of cyanobacteria and chloroplasts. Based on X-ray crystallographic, spectroscopic and genomic information, the investigator proposes to characterize molecular recognition during interprotein electron transfer and binding of quinone cofactors by photosystem I proteins. On the reducing side of photosystem I, PsaD is essential for docking of ferredoxin. Using molecular genetics and protein chemistry, the investigator has identified basic residues that are exposed on the ferredoxin-interacting surface of PsaD. He will use site-directed mutagenesis and biochemical studies to examine the role of these basic residues in interaction with ferredoxin. Photosystem I contains two phylloquinone molecules, one of which serves as the redox center A1 which transfers electrons from the A0 chlorophyll a to the FX iron-sulfur cluster. Based on the available structural and spectroscopic information, the investigator proposes that the conserved YW sequences in the last stromal loop of the PsaA and PsaB proteins are essential components of the phylloquinone-binding sites. Mutations in these residues will be generated to identify the A1 binding subunit. The investigator will manipulate the phylloquinone biosynthetic pathway using molecular genetics. He will delete the menB gene that encodes naphtholate synthase. The resulting mutants will be used to examine phylloquinone in vivo 2. Non Technical Electron transfer reactions are crucial steps in photosynthesis, respiration, and many other biochemical pathways. Energy generation in a cell is dependent on electron transfer across membranes. The investigator will study the molecular basis of protein interactions and function during photosynthetic electron transfer. This research will attempt to unravel the mechanisms of efficient capture of light energy and its storage by living systems. Ox ygenic photosynthesis in plants, algae and cyanobacteria is the major source of biological energy and oxygen on the earth. The investigator's work will increase the knowledge of photosynthesis and will provide information that can potentially be used for genetic manipulation photosynthesis in crop plants
