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Molecular and Cellular Biology, March 2002, p. 1639-1655, Vol. 22, No. 6
0270-7306/02/$04.00+0     DOI: 10.1128/MCB.22.6.1639-1655.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Peroxisomal Targeting Signal Receptor Pex5p Interacts with Cargoes and Import Machinery Components in a Spatiotemporally Differentiated Manner: Conserved Pex5p WXXXF/Y Motifs Are Critical for Matrix Protein Import

Hidenori Otera,1,2 Kiyoko Setoguchi,1 Maho Hamasaki,1 Toshitaka Kumashiro,1 Nobuhiro Shimizu,1 and Yukio Fujiki1,2*

Department of Biology, Faculty of Sciences, Kyushu University Graduate School, Fukuoka 812-8581,1 SORST, Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012, Japan2

Received 28 September 2001/ Returned for modification 19 November 2001/ Accepted 12 December 2001

Two isoforms of the peroxisomal targeting signal type 1 (PTS1) receptor, termed Pex5pS and (37-amino-acid-longer) Pex5pL, are expressed in mammals. Pex5pL transports PTS1 proteins and Pex7p-PTS2 cargo complexes to the initial Pex5p-docking site, Pex14p, on peroxisome membranes, while Pex5pS translocates only PTS1 cargoes. Here we report functional Pex5p domains responsible for interaction with peroxins Pex7p, Pex13p, and Pex14p. An N-terminal half, such as Pex5pL(1-243), comprising amino acid residues 1 to 243, bound to Pex7p, Pex13p, and Pex14p and was sufficient for restoring the impaired PTS2 import of pex5 cell mutants, while the C-terminal tetratricopeptide repeat motifs were required for PTS1 binding. N-terminal Pex5p possessed multiple Pex14p-binding sites. Alanine-scanning analysis of the highly conserved seven (six in Pex5pS) pentapeptide WXXXF/Y motifs residing at the N-terminal region indicated that these motifs were essential for the interaction of Pex5p with Pex14p and Pex13p. Moreover, mutation of several WXXXF/Y motifs did not affect the PTS import-restoring activity of Pex5p, implying that the binding of Pex14p to all of the WXXXF/Y sites was not a prerequisite for the translocation of Pex5p-cargo complexes. Pex5p bound to Pex13p at the N-terminal part, not to the C-terminal SH3 region, via WXXXF/Y motifs 2 to 4. PTS1 and PTS2 import required the interaction of Pex5p with Pex14p but not with Pex13p, while Pex5p binding to Pex13p was essential for import of catalase with PTS1-like signal KANL. Pex5p recruited PTS1 proteins to Pex14p but not to Pex13p. Pex14p and Pex13p formed a complex with PTS1-loaded Pex5p but dissociated in the presence of cargo-unloaded Pex5p, implying that PTS cargoes are released from Pex5p at a step downstream of Pex14p and upstream of Pex13p. Thus, Pex14p and Pex13p very likely form mutually and temporally distinct subcomplexes involved in peroxisomal matrix protein import.


* Corresponding author. Mailing address: Department of Biology, Faculty of Sciences, Kyushu University Graduate School, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan. Phone: 81-92-642-2635. Fax: 81-92-642-4214. E-mail: yfujiscb{at}mbox.nc.kyushu-u.ac.jp.


Molecular and Cellular Biology, March 2002, p. 1639-1655, Vol. 22, No. 6
0022-538X/02/$04.00+0     DOI: 10.1128/MCB.22.6.1639-1655.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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