Topology of Photosynthetic Proteins

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The general objective of this project is to understand the functional organization of energy-transducing membranes. The subject of the immediate investigation is the photosynthetic membrane, and in particular the proteins of the reaction center designated photosystem I. At the heart of energy transduction in this reaction center are two large proteins coded for by chloroplast genes. It is currently believed that these large membrane proteins are comprised of membrane-traversing hydrophobic alpha-helical amino acid sequences connected by hydrophilic portions that protrude from one or the other side of the surface of the membrane. The first question to be addressed experimentally is: How are the two large PSI reaction center proteins disposed in thylakoid membranes? This is to be approached by using small synthetic polypeptides corresponding to amino acid sequences in predicted hydrophilic regions of the protein, to generate peptide-specific antibodies. Electron microscope immunocytochemistry and other methods will be used to determine the topology of the proteins in the membrane. This information is to be used as a basis for other experimental approaches to study the relationships of these proteins to other photosynthetic membrane proteins, and to advance the understanding of energy transduction and electron transport in membranes.