Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/16/1999
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Details regarding the targeting signals and trafficking pathways for proteins destined for the peroxisomal boundary membrane are considerably less well defined than those for matrix proteins. For example, it is not known whether most or all peroxisome membrane proteins (PMPs) are synthesized on polysomes in the cytosol and post-translationally added either directly or indirectly to pre-existing peroxisomes. Recent studies with yeast indicate that "functional" (catalytic) PMPs sort directly to peroxisomes, whereas PMPs involved in biogenesis (peroxins) are sorted to peroxisomes via the ER. The cottonseed 31-kDa peroxisomal membrane protein (PMP) is a novel isoform of ascorbate peroxidase (pAPX) that functions in NAD+ regeneration and protection against reactive oxygen species. We employed both in vivo and in vitro approaches to elucidate the intracellular sorting of pAPX to the boundary membrane of peroxisomes. Immunofluorescence microscopic analysis of BY-2 cells transformed transiently with epitope-tagged pAPX revealed that the protein was localized to peroxisomes and to a subdomain of the ER, termed peroxisomal ER (pER). Results from mutagenesis studies indicated that the unique C-terminal domain of pAPX possesses the topogenic information both necessary and sufficient for sorting to peroxisomes and pER. Interestingly, the sorting of a chimeric protein containing the pAPX C-terminal domain caused a profound, aggregation of peroxisomes and pER. This aggregation phenomenon is due to the oligomerization of cytosolic-facing, tail-anchored membrane proteins known as membrane "zippering".