The AAA-type ATPases Pex1p and Pex6p and their role in peroxisomal matrix protein import in Saccharomyces cerevisiae.

The recognition of the conserved ATP-binding domains of Pex1p, p97 and NSF led to the discovery of the family of AAA-type ATPases. The biogenesis of peroxisomes critically depends on the function of two AAA-type ATPases, namely Pex1p and Pex6p, which provide the energy for import of peroxisomal matrix proteins. Peroxisomal matrix proteins are synthesized on free ribosomes in the cytosol and guided to the peroxisomal membrane by specific soluble receptors. At the membrane, the cargo-loaded receptors bind to a docking complex and the receptor-docking complex assembly is thought to form a dynamic pore which enables the transition of the cargo into the organellar lumen. The import cycle is completed by ubiquitination- and ATP-dependent dislocation of the receptor from the membrane to the cytosol, which is performed by the AAA-peroxins. Receptor ubiquitination and dislocation are the only energy-dependent steps in peroxisomal protein import. The export-driven import model suggests that the AAA-peroxins might function as motor proteins in peroxisomal import by coupling ATP-dependent removal of the peroxisomal import receptor and cargo translocation into the organelle.