Neue Enzyme für ein altes Organell: Kryptische peroxisomale Lokalisationssignale

Peroxisomes are near-ubiquitous eukaryotic organelles with a general function in the β- oxidation of fatty acids and hydrogen peroxide detoxification. Additionally peroxisomes exhibit more specific metabolic function in different organisms including parts of the reactions of the glyoxylate cycle in plants and fungi and the production of secondary metabolites. A special type of peroxisomes has been identified in trypanosomes. In these parasites the majority of glycolytic enzymes is localized in peroxisomes. All types of peroxisomes are characterized by a unique protein import system. Peroxisomal matrix proteins contain C-terminal or N-terminal PTS (peroxisomal targeting signal) motifs (C-terminal: PTS1; N-Terminal: PTS2), which are recognized by soluble receptors mediating the import of fully folded and even oligomeric proteins. Studies on mRNA processing in the plant pathogenic fungus Ustilago maydis lead to the unexpected discovery of isoforms of glycolytic enzymes harboring PTS1 motifs. These isoforms result from alternative splicing and translational read-through, respectively. A bioinformatic survey revealed the presence of such isoforms in many fungal species, although the mechanisms giving rise to PTS1 motifs vary between species. Some glycolytic enzymes were shown to possess low efficiency PTS1 motifs differing from the PTS1 consensus sequence. These motifs might also lead to dual cytoplasmic and peroxisomal targeting similar to the already described mechanisms. More detailed analysis of peroxisomes in U. maydis established additional functions of these organelles in sugar metabolism and pathogenic development beside their prominent role in the breakdown of fatty acids. Moreover, it could be demonstrated that peroxisomes participate in the production of glycolipids in U. maydis. The data obtained here suggests novel metabolic functions for peroxisomes at least in fungi. The identification of cryptic PTS1 motifs in glycolytic enzymes in fungi indicates that peroxisomes of other organisms likely contain a variety of unexpected proteins.