Biogenesis of beta-barrel proteins of the outer membranes of endosymbiotic organelles

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The outer membranes (OM) of the endosymbiotically derived organelles mitochondria and plastids constitute the communication platform between these organelles and the other cell compartments. Consequentially, the proteomes of these membranes were adopted during evolution to fulfill the imposed requirements ranging from exchange of solutes and macromolecules to lipid transfer and signal transduction. The vast majority of organeller proteins are encoded in the nucleus and synthesized on cytosolic ribosomes. A unique group of such organellar proteins are those with beta-barrel architecture that are found in the outer membranes of both organelles. The delivery of such OM proteins from the cytosol to their target membrane has to be tightly regulated especially in plant cells where the two organelles have to be supplied in parallel while keeping targeting specificity. The targeting factors that define this specificity are not yet known. We will identify such factors in yeast and plant cells, and will dissect their function in targeting of proteins in general and for the specific delivery of beta-barrel proteins to the correct organelle.