Purification of a subset of Saccharomyces cerevisiae peroxisomal proteins
Guha, Tuhin Kumar
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Peroxisomes are ubiquitous and are considered to be vital organelles in eukaryotic cells; however, unlike mitochondria and chloroplast, they lack DNA and a protein secretory apparatus. Therefore, peroxisome biogenesis requires a group of proteins called peroxins encoded by the pex genes. Out of the thirty two known peroxins discovered so far, a subset of peroxins including enzyme IDP3 and proteins namely, PEX18, PEX21 and PEX6 were chosen for this research. IDP3 plays a vital role in peroxisomal metabolism where it generates NADPH which in turn is needed by the peroxisomal enzymes to degrade unsaturated fatty acids. PEX18 and PEX21 are mutually redundant but essential for the transport of PTS2 targeted proteins into the peroxisome. PEX6 is involved in the ATP-dependent recycling of the protein receptor from the peroxisomal membrane to the cytosol. Expression plasmids were constructed that encoded each of these proteins in tandem with a histidine tag at either or both the amino and carboxy terminals of the protein. The purification of IDP3 was achieved using affinity chromatography on a nickel resin. After several unsuccessful attempts using ion exchange and size exclusion chromatography, PEX18 and PEX21 were purified by nickel affinity chromatography after denaturation to expose their His tags. The expression of PEX6 was poor by comparison with the other proteins and the low amount of protein precluded a complete purification. Future work will involve crystal screen trials, X-ray diffraction and structure refinement.