Towards the molecular architecture of the peroxisomal receptor docking complex

Import of yeast peroxisomal matrix proteins is initiated by cytosolic receptors, which specifically recognize and bind the respective cargo proteins. At the peroxisomal membrane, the cargo-loaded receptor interacts with the membrane docking complex, composed of Pex14p, Pex17p and Pex13p. Previous data suggest that this interaction triggers the formation of an import pore for further translocation of the cargo. The mechanistic principles and the underlying mechanism are however unclear, mainly because structures of higher order assemblies are still lacking. Here, using an integrative approach, we provide the first structural characterization of the major components of the peroxisomal docking complex Pex14p/Pex17p, in a native bilayer environment and reveal its subunit organization. Our data show that three copies of Pex14p and a single copy of Pex17p assemble to form a 20 nm rod-like particle. The different subunits are arranged in a parallel manner, showing interactions along their complete sequences and providing receptor binding-sites on both membrane sides. The long rod facing the cytosol is mainly formed by the coiled-coil domains of Pex14p and Pex17p, possibly providing the necessary structural support for the formation of the import pore. Further implications of Pex14p/Pex17p for formation of the peroxisomal translocon are discussed.