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J. Biol. Chem., Vol. 281, Issue 15, 10196-10205, April 14, 2006

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Functional Domains and Dynamic Assembly of the Peroxin Pex14p, the Entry Site of Matrix Proteins^*

Ryota Itoh and Yukio Fujiki¹

From the Department of Biology, Faculty of Sciences, Kyushu University Graduate School, Fukuoka 812-8581, Japan and SORST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan

The 41-kDa membrane-anchored peroxin Pex14p functions as the peroxisome targeting signal (PTS) receptor-mediated, initial import site for matrix proteins. We here identify the functional domains of Pex14p involved in the assembly of import site subcomplexes. The minimal region of Pex14p required for restoring impaired protein import in pex14 Chinese hamster ovary cell mutant lies at residues 21-260 in the primary sequence. A highly conserved N-terminal region, encompassing residues 21-70, interacts with the PTS1 receptor Pex5p, Pex13p, and Pex19p that is essential for membrane biogenesis. N-terminal residues 21-140, including a hydrophobic segment at 110-138, function as a topo-genic sequence. Site-directed mutagenesis, size fractionation, and chemical cross-linking analyses demonstrate that the coiled-coil domain at residues 156-197 regulates homodimerization of Pex14p. Moreover, AXXXA and GXXXG motifs in the transmembrane segment mediate homomeric oligomerization of Pex14p, giving rise to assembly of high molecular mass complexes and thereby assuring Pex13p-dependent localization of Pex14p to peroxisomes. Pex5p, Pex13p, and Pex19p bind to Pex14p homo-oligomers with different molecular masses, whereas cargo-unloaded Pex5p apparently disassembles Pex14p homo-oligomers. Thus, Pex14p most likely forms several distinct peroxin complexes involved in peroxisomal matrix protein import.

Received for publication, January 6, 2006

^* This work was supported in part by a SORST grant from the Science and Technology Agency of Japan; grants-in-aid for Scientific Research, Grant of National Project on Protein Structural and Functional Analyses, The 21st Century COE Program from The Ministry of Education, Culture, Sports, Science, and Technology of Japan; and grants from the Uehara Memorial Foundation, Japan Foundation for Applied Enzymology, and the Takeda Science Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental information.

¹ To whom correspondence should be addressed: Dept. of Biology, Faculty of Sciences, Kyushu University Graduate School, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan. Tel.: 81-92-642-2635; Fax: 81-92-642-4214; E-mail: yfujiscb{at}mbox.nc.kyushu-u.ac.jp.

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