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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

The DEG15 Serine Protease Cleaves Peroxisomal Targeting Signal 2-Containing Proteins in Arabidopsis^1,[OA]

Department of Physiology and Plant Biochemistry, University of Konstanz, DE–78457 Konstanz, Germany (H.S., P.F.H., I.A.); and Biologikum Weihenstephan, Technical University of Munich, DE–85350 Freising, Germany (C.G.)

Two distinct peroxisomal targeting signals (PTSs), the C-terminal PTS1 and the N-terminal PTS2, are defined. Processing of the PTS2 on protein import is conserved in higher eukaryotes. Recently, candidates for the responsible processing protease were identified from plants (DEG15) and mammals (TYSND1). We demonstrate that plants lacking DEG15 show an expressed phenotype potentially linked to reduced β-oxidation, indicating the impact of protein processing on peroxisomal functions in higher eukaryotes. Mutational analysis of Arabidopsis (Arabidopsis thaliana) DEG15 revealed that conserved histidine, aspartic acid, and serine residues are essential for the proteolytic activity of this enzyme in vitro. This indicates that DEG15 and related enzymes are trypsin-like serine endopeptidases. Deletion of a plant-specific stretch present in the protease domain diminished, but did not abolish, the proteolytic activity of DEG15 against the PTS2-containing glyoxysomal malate dehydrogenase. Fluorescence microscopy showed that a DEG15-green fluorescent protein fusion construct is targeted to peroxisomes in planta. In vivo studies with isolated homozygous deg15 knockout mutants and complemented mutant lines suggest that this enzyme mediates general processing of PTS2-containing proteins.

² Present address: Centre for Blood Research, University of British Columbia, 4.401 Life Sciences Centre, 2350 Health Sciences Mall, Vancouver, British Columbia, Canada V6T 1Z3.

The author responsible for the distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Iwona Adamska (iwona.adamska{at}uni-konstanz.de).

^[OA] Open access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.125377

^* Corresponding author; e-mail iwona.adamska{at}uni-konstanz.de.

Received June 26, 2008; accepted October 20, 2008; published October 24, 2008.

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