title: The relevance of the non-canonical PTS1 of peroxisomal catalase.
abstract: Catalase is sorted to peroxisomes via a C-terminal peroxisomal targeting signal 1 (PTS1), which binds to the receptor protein Pex5. Analysis of the C-terminal sequences of peroxisomal catalases from various species indicated that catalase never contains the typical C-terminal PTS1 tripeptide-SKL, but invariably is sorted to peroxisomes via a non-canonical sorting sequence. We analyzed the relevance of the non-canonical PTS1 of catalase of the yeast Hansenula polymorpha (-SKI). Using isothermal titration microcalorimetry, we show that the affinity of H. polymorpha Pex5 for a peptide containing -SKI at the C-terminus is 8-fold lower relative to a peptide that has a C-terminal -SKL. Fluorescence microscopy indicated that green fluorescent protein containing the -SKI tripeptide (GFP-SKI) has a prolonged residence time in the cytosol compared to GFP containing -SKL. Replacing the -SKI sequence of catalase into -SKL resulted in reduced levels of enzymatically active catalase in whole cell lysates together with the occurrence of catalase protein aggregates in the peroxisomal matrix. Moreover, the cultures showed a reduced growth yield in methanol-limited chemostats. Finally, we show that a mutant catalase variant that is unable to properly fold mislocalizes in protein aggregates in the cytosol. However, by replacing the PTS1 into -SKL the mutant variant accumulates in protein aggregates inside peroxisomes. Based on our findings we propose that the relatively weak PTS1 of catalase is important to allow proper folding of the enzyme prior to import into peroxisomes, thereby preventing the accumulation of catalase protein aggregates in the organelle matrix.
authors.affiliation: European Molecular Biology Laboratory, Structural Biology Unit, Notkestrasse 85, 22603, Hamburg, Germany.
authors.forename: Chris
authors.initials: C
authors.lastname: Williams
authors.forename: Eda
authors.initials: E
authors.lastname: Bener Aksam
authors.forename: Katja
authors.initials: K
authors.lastname: Gunkel
authors.forename: Marten
authors.initials: M
authors.lastname: Veenhuis
authors.forename: Ida J
authors.initials: IJ
authors.lastname: van der Klei
mesh_terms: D000595:Amino Acid Sequence; D002151:Calorimetry; D002374:Catalase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D005656:Fungal Proteins; D049452:Green Fluorescent Proteins / Q000378:metabolism; D000432:Methanol / Q000494:pharmacology; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism; D000074435:Peroxisome-Targeting Signal 1 Receptor; D020675:Peroxisomes / Q000201:enzymology* / Q000648:ultrastructure; D010843:Pichia / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development; D011485:Protein Binding / Q000187:drug effects; D021382:Protein Sorting Signals; D020836:Protein Structure, Quaternary; D021381:Protein Transport / Q000187:drug effects; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D013329:Structure-Activity Relationship; D013997:Time Factors
chemical_list: D005656:Fungal Proteins; D009842:Oligopeptides; C000614263:PEX5 protein, Pichia pastoris; D000074435:Peroxisome-Targeting Signal 1 Receptor; D021382:Protein Sorting Signals; D018160:Receptors, Cytoplasmic and Nuclear; D049452:Green Fluorescent Proteins; D002374:Catalase; D000432:Methanol