Pex9p is a novel yeast peroxisomal import receptor for PTS1-proteins

Peroxisomal proteins carrying a type 1 peroxisomal targeting signal (PTS1) are recognized by the well-conserved cycling import receptor Pex5p. Yeast YMR018w gene codes for a Pex5p paralog and novel peroxin that is involved in peroxisomal import of a subset of matrix proteins. The novel peroxin was designated Pex9p and it interacts with the docking protein Pex14p and a subclass of PTS1-containing peroxisomal matrix enzymes. Unlike Pex5p, Pex9p is not expressed in glucoseor ethanol-grown cells, but it is strongly induced by oleate. Under these conditions, Pex9p acts as a cytosolic and membrane-bound peroxisome import receptor for both malate synthase isoenzymes, Mls1p and Mls2p. The inducible Pex9p-dependent import pathway provides a rationale for the oleate-inducible peroxisomal targeting of malate synthases. The existence of two distinct PTS1-receptors, in addition to two PTS2-dependent import routes, contributes to the adaptive metabolic capacity of peroxisomes in response to environmental changes and underlines the role of peroxisomes as multi-purpose organelles. The discovered differential import into peroxisomes contributes to the molecular understanding of how regulated protein targeting can adapt the function of organelles according to cellular needs. Jo ur na l o f C el l S ci en ce • A dv an ce a rt ic le