Multiple targeting modules on peroxisomal proteins are not redundant: discrete functions of targeting signals within Pmp47 and Pex8p.
Several peroxisomal proteins have two nonoverlapping targeting signals. These signals have been termed "redundant" because targeting can still occur with only one signal. We now report that separate targeting motifs within both Pmp47 and Pex8 provide complementary function. Pmp47 is an ATP translocator that contains six transmembrane domains (TMDs). We had previously shown that the TMD2 region (termed TMD2R, consisting of TMD2 and a short adjacent segment of cytosolic loop) was required for targeting to proliferated peroxisomes in Saccharomyces cerevisiae. We now report that the analogous TMD4R, which cannot target to proliferated peroxisomes, targets at least as well, or much better (depending on strain and growth conditions) in cells containing only basal (i.e., nonproliferated) peroxisomes. These data suggest differences in the targeting pathway among peroxisome populations. Pex8p, a peripheral protein facing the matrix, contains a typical carboxy terminal targeting sequence (PTS1) that has been shown to be nonessential for targeting, indicating the existence of a second targeting domain (not yet defined in S. cerevisiae); thus, its function was unknown. We show that targeting to basal peroxisomes, but not to proliferated peroxisomes, is more efficient with the PTS1 than without it. Our results indicate that multiple targeting signals within peroxisomal proteins extend coverage among heterogeneous populations of peroxisomes and increase efficiency of targeting in some metabolic states.
Wang
Xiaodong
X
Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9041, USA.
McMahon
Moira A
MA
Shelton
Shary N
SN
Nampaisansuk
Mongkol
M
Ballard
Johnathan L
JL
Goodman
Joel M
JM
D002455:Cell Division; D003593:Cytoplasm / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D005656:Fungal Proteins / Q000502:physiology*; D017353:Gene Deletion; D005947:Glucose / Q000378:metabolism; D005990:Glycerol / Q000737:chemistry; D008565:Membrane Proteins / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000502:physiology*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D019301:Oleic Acid / Q000737:chemistry; D000074401:Peroxins; D020675:Peroxisomes / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology*; D015398:Signal Transduction; D013347:Subcellular Fractions
D005656:Fungal Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C066456:PMP47 protein, Candida boidinii; D000074401:Peroxins; C404515:Pex8 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D019301:Oleic Acid; D004247:DNA; D005947:Glucose; D005990:Glycerol