Import of peroxisomal membrane proteins: the interplay of Pex3p- and Pex19p-mediated interactions.

In contrast to the molecular mechanisms underlying import of peroxisomal matrix proteins, those involving the transport of membrane proteins remain rather elusive. At present, two targeting routes for peroxisomal membrane proteins (PMPs) have been depicted: class I PMPs are targeted from the cytoplasm directly to the peroxisome membrane, and class II PMPs are sorted indirectly to peroxisomes via the endoplasmic reticulum (ER). In addition, three peroxins--Pex3p, Pex16p, and Pex19p - have been identified as essential factors for PMP assembly in several species including humans: Pex19p is a predominantly cytoplasmic protein that shows a broad PMP-binding specificity; Pex3p serves as the membrane-anchoring site for Pex19p; and Pex16p - a protein absent in most yeasts--is thought to provide the initial scaffold for recruiting the protein import machinery required for peroxisome membrane biogenesis.

Functional domain mapping of peroxin Pex19p: interaction with Pex3p is essential for function and translocation.

The peroxin Pex19p functions in peroxisomal membrane assembly. Here we mapped functional domains of human Pex19p comprising 299 amino acids. Pex19p mutants deleted in the C-terminal CAAx farnesylation motif, the C-terminal 38 amino acid residues and the N-terminal 11 residues, maintained peroxisome-restoring activity in pex19 cells.

In vitro transport of membrane proteins to peroxisomes by shuttling receptor Pex19p.

The peroxin Pex19p comprising 299 amino acids functions in peroxisomal membrane assembly. We here developed a cell-free system for transport of membrane proteins to peroxisomes. Pex19p interacts with multiple membrane peroxins, including other membrane biogenesis peroxins, Pex16p and Pex26p, involved in matrix protein import.