Structural domains that contribute to substrate specificity in facilitated glucose transporters are distinct from those involved in kinetic function: studies with GLUT-1/GLUT-2 chimeras.

GLUT-2 differs from other members of the facilitated glucose transporter family because it transports a wider range of substrates and exhibits a higher Km for transport of glucose analogs such as 2-deoxyglucose (2-DOG). In order to investigate the structural determinants of the unique substrate specificity and kinetic function of GLUT-2, recombinant adenoviruses were used to express native, mutant, and chimeric glucose transporters in the kidney cell line CV-1, yielding the following key observations. (1) A chimera consisting of GLUT-1 with the C-terminal tail of GLUT-2 had a Km for 2-DOG of 9.9 +/- 1.5 that was intermediate between that of native GLUT-1 (3.7 +/- 0.4) and native GLUT-2 (26.3 +/- 3.3). In contrast to the effect of the GLUT-2 C terminus on Km for 2-DOG, this substitution did not confer enhanced uptake of three alternative substrates (fructose, arabinose, or streptozotocin) which are transported efficiently by native GLUT-2 but not by GLUT-1. (2) A chimera consisting of GLUT-2 with the N-terminal 87 amino acids of GLUT-1 exhibited no change in Km for 2-DOG relative to native GLUT-2 but exhibited a significant reduction in capacity for transport of the three alternative substrates. (3) Mutation of asparagine 62 in GLUT-2 to glutamine produced a transporter lacking its N-linked oligosaccharide that exhibited a 2.5-fold increase in Km for 2-DOG but equally efficient transport of the three alternative substrates relative to native GLUT-2. These data provide insight into structural domains that affect substrate specificity in facilitated glucose transporters and demonstrate that they are distinct from elements involved in glucose transport kinetics.

Duke Scholars

Author Christopher Bang Newgard Pharmacology & Cancer Biology