Abstract
Saccharomyces cerevisiae Aat2p contains a peroxisomal targeting signal type‐1 and localizes to peroxisomes in oleate‐grown cells, but not in glucose‐grown cells. Here, we have investigated Aat2p from the yeast Hansenula polymorpha, which lacks a recognizable peroxisomal targeting signal. Aat2p tagged with GFP at its C terminus displays a dual cytosol‐peroxisome localization in ethanol‐grown cells. The partial peroxisomal localization of Aat2p persisted in the absence of the classical cycling receptors Pex5p and Pex7p but Aat2p targeting to peroxisomes was reduced in cells deleted for the matrix protein import factors PEX1, PEX2 and PEX13. Furthermore, we demonstrate that Aat2p targeting to peroxisomes requires Pex20p. Together, our data identify a Pex20p‐dependent pathway for targeting Aat2p to peroxisomes.
Highlights
The partial peroxisomal localization of Aat2p persisted in the absence of the classical cycling receptors Pex5p and Pex7p but Aat2p targeting to peroxisomes was reduced in cells deleted for the matrix protein import factors PEX1, PEX2 and PEX13
We demonstrate that Hansenula polymorpha Aat2p (HpAat2p), which lacks a recognizable Peroxisome Targeting Signal (PTS), displays dual localization to the cytosol and peroxisomes in glucose and ethanol-grown cells, whereas it is cytosolic in methanol-grown cells
Pex20p from the yeast Yarrowia lipolytica binds to the PTS2 protein thiolase in a PTS2-independent manner [44]
Summary
Our data identify a Pex20p-dependent pathway for targeting Aat2p to peroxisomes. Pex5p recruits cargo proteins to the peroxisomal matrix by means of a C-terminal tetratricopeptide repeat domain, which interacts with the PTS1 sequence [10]. A second PTS (PTS2) was identified in a subset of peroxisomal matrix proteins, bearing the Nterminal consensus sequence (R/K)(L/V/I)X5(H/Q)(L/ A) [11,12]. Unlike the PTS1 pathway, PTS2 import requires the Pex20p family of coreceptor proteins in yeast and fungi [13,14] or a long isoform of Pex5p in higher eukaryotes [15]. Abbreviations HpAat2p, Hansenula polymorpha Aat2p; PCR, polymerase chain reactions; PNS, Post Nuclear Supernatant; PTS, peroxisome targeting signal; Pyc-1, pyruvate carboxylase-1; TCA, trichloroacetic acid
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