The subcellular location of several integral peroxisomal membrane proteins in plants, yeast and mammalian cells
Peroxisomes are ubitquitous eukaryotic organelles that participate in a wide range of cellular functions including fatty acid [beta]-oxidation, photorespiration and stress signaling. Although, the metabolic functions of peroxisomes have been well studied, much less is known about the mechanisms by which protein constituents including enzymatic components are acquired from their site of synthesis in the cytosol and brought to peroxisomes. This is especially true for the acquisition of peroxisomal membrane proteins (PMPs). The purpose of this study was to gain a better understanding of whether there is conservation in the sorting mechanisms, e.g., targeting signals, cognate receptors and insertion apparatus, responsible for localizing proteins to the peroxisomal boundary membrane in evolutionarily diverse organisms. Towards this end, various PMPs including cottonseed ascorbate peroxidase, ' Arabidopsis thaliana' PMP22, 'Saccharomyces cerevisiae' PMP22 and 'S. cerevisiae' Pex15p, were individually expressed as either fusions with the green fluorescent protein (GFP) or tagged with the myc epitope, in tobacco BY-2, 'S. cerevisiae' and human cancerous (HeLa) cells. Immunofluorescence microscopic analysis of the resulting transformed cells indicated that most of the PMPs examined were localized to peroxisomes, although on occasion sorting to a number of other subcellular sites including mitochondria and endoplasmic reticulum was also observed. Taken together, these data indicate that the mechanisms responsible for sorting PMPs are relatively well conserved among diverse species, although some mechanistic differences do exist. These data also suggest that the mechanisms involved in the production of nascent peroxisomes are conserved among, at least, plants, yeast and mammals.