Presence of isomaltose transporters in Aspergilli demonstrated through nuclear translocation assays of the transcription factor AmyR.

Abstract

Maltose is readily incorporated into Aspergillus oryzae cells. In contrast, isomaltose is unlikely to be incorporated into both A. oryzae and Aspergillus nidulans, even though extremely low concentrations of isomaltose can induce the nuclear translocation of AmyR. This suggests the presence of sensor-like proteins or isomaltose transporters in both Aspergilli. In this study, we showed that isomaltose can be incorporated via sugar/H+ symporters using AmyR nuclear translocation assays. Assuming that sugar transporters are proton-coupled symporters, we examined the effect of the protonophore carbonyl cyanide m-chlorophenyl hydrazone on isomaltose-induced AmyR nuclear translocation. Consequently, AmyR nuclear translocation was impaired by the addition of the protonophore in A. oryzae. This was confirmed under high pH conditions where AmyR nuclear translocation was abrogated in both Aspergilli. These results suggest that instead of sensors, isomaltose is most likely incorporated by sugar/H+ symporters with low isomaltose transport activity, triggering isomaltose-induced AmyR nuclear translocation.