Expression and Characterization of Rice Disproportionating Enzymes

Abstract

This work aims to characterize disproportionating enzyme (DPE1) and its isoform DPE2 in rice. Rice DPE genes (OsDPE1 and OsDPE2) were cloned and expressed in E. coli. The OsDPE1 and OsDPE2 genes encode proteins of 594 and 946 amino acids with a calculated molecular mass of 67 kDa and 108 kDa, respectively. Purified recombinant OsDPE1 and OsDPE2 showed highest activity at around pH 7.0 and pH 6.0-7.0, respectively. The optimum reaction temperature was 30°C for OsDPE1 and 39°C for OsDPE2. Recombinant OsDPE1 disproportionates maltotriose to produce glucose and maltopentaose, and thus shares the defining behavior of D-enzymes. In our experiments, recombinant OsDPE2 catalyzed the glucose transfer reaction from maltose to an acceptor molecule such as glycogen. We also characterized the differences between the diurnal transcription profiles of OsDPE1 and OsDPE2 in rice leaves and seeds, and their temporal expression levels in developing rice seeds.