Identification and Characterization of the Human Orthologue of Yeast Pex14p

Abstract

Pex14p is a central component of the peroxisomal protein import machinery, which has been suggested to provide the point of convergence for PTS1-and PTS2-dependent protein import in yeast cells. Here we describe the identification of a human peroxisome-associated protein (HsPex14p) which shows significant similarity to the yeast Pex14p. HsPex14p is a carbonate-resistant peroxisomal membrane protein with its C terminus exposed to the cytosol. The N terminus of the protein is not accessible to exogenously added antibodies or protease and thus might protrude into the peroxisomal lumen. HsPex14p overexpression leads to the decoration of tubular structures and mislocalization of peroxisomal catalase to the cytosol. HsPex14p binds the cytosolic receptor for the peroxisomal targeting signal 1 (PTS1), a result consistent with a function as a membrane receptor in peroxisomal protein import. Homo-oligomerization of HsPex14p or interaction of the protein with the PTS2-receptor or HsPex13p was not observed. This distinguishes the human Pex14p from its counterpart in yeast cells and thus supports recent data suggesting that not all aspects of peroxisomal protein import are conserved between yeasts and humans. The role of HsPex14p in mammalian peroxisome biogenesis makes HsPEX14 a candidate PBD gene for being responsible for an unrecognized complementation group of human peroxisome biogenesis disorders.

Hansenula polymorpha Pex3p Is a Peripheral Component of the Peroxisomal Membrane

“…They conclude that although PpPex14p behaves like an integral membrane protein upon carbonate treatment, it does not contain any membranespanning regions, contrary to results published of other Pex14p homologues (e.g. human (40) and H. polymorpha (29) Pex14p). Therefore, they conclude that tight association with other integral membrane proteins probably causes the strong interaction of Pex14p with the peroxisomal membrane in P. pastoris.…”

Characterization of Peroxisomal Pex5p from Rat Liver

“…The interaction of Pex14p with the peroxisomal membrane in yeast cells is still a matter of controversy (20,38,40). However, clear results regarding the mammalian Pex14p topology have been recently published (22). The data presented by Will et al (22) strongly suggest that the N-terminal domain of human Pex14p is exposed into the lumen of the organelle.…”

“…However, clear results regarding the mammalian Pex14p topology have been recently published (22). The data presented by Will et al (22) strongly suggest that the N-terminal domain of human Pex14p is exposed into the lumen of the organelle. Based on this finding, the authors speculated that this would imply that the PTS1 receptor is in the lumen of the peroxisome at some stage of the protein import process, an hypothesis that would be in support of the "extended shuttle model of peroxisomal protein import" (15).…”

“…It was proposed by several authors that Pex13p and Pex14p represent the peroxisomal docking factors for Pex5p (13, 14, 19 -21), although recently, some doubts were raised regarding the role of Pex14p in this process (Ref. 22 and see under "Discussion"). Despite all these data, not much is known about the architecture of the peroxisomal import machinery.…”

Tetratricopeptide repeat domain of Yarrowia lipolytica Pex5p is essential for recognition of the type 1 peroxisomal targeting signal but does not confer full biological activity on Pex5p

“…Mammalian Pex5p and Pex7p have recently been reported to interact with Pex14p [38][39][40][41]. Loss of function of either PTS receptor leads to disease states in humans, causing neonatal adrenoleucodystrophy and Zellweger syndrome in Pex5p mutation [11] and rhizomelic chondrodysplasia punctata in Pex7p deficiency [23][24][25].…”