Identification of the structural determinants for efficient glucose transport via segment swapping between two fungal glucose transporters

Abstract

Glucose transporters mediate the intracellular uptake of glucose and play important roles in glucose metabolism and signaling. Our understanding of the structural basis for a variety of glucose transporters is, however, still limited. In this study, we presented that the glucose transporter Hgt-1, obtained from the filamentous fungus Neurospora crassa, exhibited much higher glucose transport activity than the other sugar transporter Stp1, obtained from Trichoderma reesei, although they shared high sequence identity of 75.9%. To identify the structural determinants for differential glucose transport capability displayed by Stp1 and Hgt-1, segment swapping was performed by replacing specific sequence regions of Stp1 with the corresponding sequences of Hgt-1. Investigation of the glucose transport capability of the resulting chimeric transporters revealed that replacement of a N- or a C-terminal segment of Stp1, located on the intracellular side, with that of Hgt-1 can apparently improve its transport capability. The combined swapping of these two segments further enhanced the transport capability of Stp1 to a level almost comparable to that of Hgt-1. However, deletion of the C-terminal 32 residues abolished the transport capability of Stp1, whereas deletion of the C-terminal 16 residues apparently improved its transport capability. These results provide insight into the roles of intracellular N- and C-termini of glucose transporters in glucose transport.