Poster: Protein Targeting & Vesicular Trafficking

Abs # 1181: Molecular mechanism for catalase import into peroxisomes in Arabidopsis thaliana

Presenter:	Kamigaki, Akane , akaneka@hiroshima-u.ac.jp
Authors	Kamigaki, Akane  (A)   Mano, Shoji  (B)   Nito, Kazumasa  (B)   Hayashi, Makoto  (B)   Nishimura, Mikio  (B)   Esaka, Muneharu  (A)
Affiliations:	(A): Faculty of Applied Biological Science, Hiroshima University (B): Department of Cell Biology, National Institute for Basic Biology

Most peroxisomal proteins have peroxisomal targeting signal present at the C- (PTS1) or N-terminus (PTS2). The PTS1 and PTS2 are recognized by specific receptors Pex5p and Pex7p, respectively. The PTS-containing proteins are delivered to peroxisomal membrane and translocated across the membrane via a translocation apparatus to the peroxisomal matrix. Catalase, a major peroxisomal protein, has PTS1-like motif upstream of the C terminus. So far, we attempted to identify peroxisomal targeting signal of pumpkin catalase (Cat1) by observing the cellular localization of the GFP-Cat1 fusion protein in transgenic Arabidopsis thaliana and analyzed binding of Pex5p to Cat1 by yeast two-hybrid system. These results suggested that Cat1 is transported to peroxisomes by the PTS1 system. However, the underlying molecular mechanism for catalase import remains unclear. In this study, we generated transgenic Arabidopsis thaliana overexpressing GFP-Cat1 in which the Pex5p or Pex7p has been additively knocked out by RNAi method. Then, we observed the cellular localization of Cat1 in these transgenic Arabidopsis thaliana. Peroxisomal proteins may not require their unfolding for the import. Catalase, a homotetrameric protein, may be also transported across the peroxisomal membrane without unfolding. Thus, we also examined whether the PTS1 requires tetramerization of catalase apoprotein. Furthermore, using crude extract from transgenic Arabidopsis thaliana overexpressing GFP-Cat1, we analyzed whether the Cat1 forms homotetramer in vivo by immunoblot method.