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J. Cell Biol., Volume 146, Number 1, July 12, 1999 99-112
Copyright © 1999 by The Rockefeller University Press.

Pex22p of Pichia pastoris, Essential for Peroxisomal Matrix Protein Import, Anchors the Ubiquitin-conjugating Enzyme, Pex4p, on the Peroxisomal Membrane

Antonius Kollera, William B. Snydera, Klaas Nico Fabera, Thibaut J. Wenzela, Linda Rangellb, Gilbert A. Kellerb, and Suresh Subramania
a Department of Biology, University of California San Diego, La Jolla, California 92093-0322
b Pharmacological Science, Genentech, South San Francisco, California 94080

Correspondence to: Suresh Subramani, Department of Biology, University of California San Diego, Bonner Hall, Room 3230, 9500 Gilman Drive, La Jolla, CA 92093-0322., ssubramani{at}ucsd.edu (E-mail), (619) 534-2327 (phone), (619) 534-0053 (fax)

We isolated a Pichia pastoris mutant that was unable to grow on the peroxisome-requiring media, methanol and oleate. Cloning the gene by complementation revealed that the encoded protein, Pex22p, is a new peroxin. A {Delta}pex22 strain does not grow on methanol or oleate and is unable to import peroxisomal matrix proteins. However, this strain targets peroxisomal membrane proteins to membranes, most likely peroxisomal remnants, detectable by fluorescence and electron microscopy. Pex22p, composed of 187 amino acids, is an integral peroxisomal membrane protein with its NH2 terminus in the matrix and its COOH terminus in the cytosol. It contains a 25–amino acid peroxisome membrane-targeting signal at its NH2 terminus. Pex22p interacts with the ubiquitin-conjugating enzyme Pex4p, a peripheral peroxisomal membrane protein, in vivo, and in a yeast two-hybrid experiment. Pex22p is required for the peroxisomal localization of Pex4p and in strains lacking Pex22p, the Pex4p is cytosolic and unstable. Therefore, Pex22p anchors Pex4p at the peroxisomal membrane. Strains that do not express Pex4p or Pex22p have similar phenotypes and lack Pex5p, suggesting that Pex4p and Pex22p act at the same step in peroxisome biogenesis. The Saccharomyces cerevisiae hypothetical protein, Yaf5p, is the functional homologue of P. pastoris Pex22p.

Key Words: organelle, peroxin, peroxisome, protein transport, yeast


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