Plant Peroxisome Biogenesis: Acquisition/Function of Membrane Proteins

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9728935 Trelease Eukaryotic cells contain membrane-enclosed compartments (organelles) in which various cellular functions are carried out. This isolation of various functions within physical boundaries is critical to the life of the cell: it allows the cell to regulate the functions of each compartment separately; and it prevents the contents of each compartment from interfering with others. However, it does require that the cells have mechanisms for sorting and translocating individual proteins to their proper subcellular locations. One type of intracellular compartment is the peroxisome, which occurs in virtually all eukaryotic cells. Peroxisomes participate in a very wide range of metabolic pathways, depending on the cell or tissue type in which they function. The overall goal of this project is to understand the complicated means by which peroxisomal membrane proteins (PMPs) become selectively integrated into the boundary membrane of peroxisomes (glyoxysomes) in oilseed seedlings, and to understand the functions of such PMPs within the membrane as the seedlings develop. Three specific objectives are proposed relative to the biogenesis of plant peroxisomes. The first aim is to discover the putative membrane peroxisomal targeting signal (mPTS) responsible for targeting peroxisomal ascorbate peroxidase (pAPX) to glyoxysomes, and define the topographic orientation of the protein within the membrane. This information is particularly relevant for oilseed glyoxysomes, to understand how the membrane is protected from abundant reactive oxygen species and to understand the pathway for regeneration of NAD+ required for conversion of storage oils into carbohydrates. The second aim is to test the hypothesis that a 73 kilodalton membrane-bound polypeptide, PMP73, is a novel "peroxin" which functions at the boundary membrane as a molecular chaperone in the uptake of proteins from the cytosol. The third aim is to try to discover additional plant PM Ps, using polyclonal rabbit antisera raised previously and already used successfully to discover PMP73 and pAPX. It is likely that, in addition to the overall goal of understanding peroxisomal biogenesis and function in developing oilseed seedlings, the results of these studies will provide more general insight into peroxisomal biogenesis that will be applicable to diverse species and tissues.