Trehalose synthesis in Euglena gracilis (Euglenophyceae) occurs through an enzyme complex

The aim of this study was to isolate and characterize a trehalose-synthesizing enzyme from Euglena gracilis Klebs. After purification by anion exchange chromatography, gel filtration, isoelectric focusing, and native electrophoresis, trehalose-6-phosphate synthase (TPS, EC 2.4.1.15) and trehalose-6-phosphate phosphatase (TPP, EC 3.1.3.12) activities could not be separated. Consequently, a TPS/TPP enzyme complex of about 250 kDa was suggested as responsible for trehalose synthesis in E. gracilis. The TPS activity was shown to be highly specific for glucose-6-P, and UDP-Glc was the preferred glucose donor, but GDP-Glc and CDP-Glc could also act as TPS substrates. The TPP activity was highly specific for trehalose-6-P. In vitro phosphorylation assays revealed rapid decreases in TPS and TPP activities. These changes corresponded to variations in the elution profile of gel filtration chromatography after the phosphorylation treatment. Taken together, these results suggest that the proposed TPS/TPP complex might be regulated through a protein phosphorylation/dephosphorylation-mediated mechanism that could affect the association state of the complex. Such a regulatory mechanism might lead to a rapid change in trehalose synthesis in response to variations in environmental conditions.