Identification of further important residues within the Glut4 carboxy-terminal tail which regulate subcellular trafficking

The insulin-responsive glucose transporter, Glut4, exhibits a unique subcellular distribution such that in the absence of insulin >95% of the protein is stored within intracellular membranes. In response to insulin, Glut4 exhibits a large mobilisation to the plasma membrane. Studies of the amino acid motifs which regulate the unique trafficking of Glut4 have identified several key residues within the soluble cytoplasmic N-and C-terminal domains of Glut4, Of particular note is a Leu-498Leu-499 motif within the C-terminal domain that has been proposed to regulate both internalisation from the plasma membrane and sorting to an insulin-sensitive compartment, In this study, we have examined the role of the adjacent amino acids (Glu-491, Glu-492 and Glu-493) by their sequential replacement,vith Ala, Our results are consistent with the notion that Glu-491 and Glu-493 play an important role in the sub-endosomal trafficking of Glut4, as substitution of these residues with Ala results in increased levels of these proteins at the cell surface, reduced insulin-stimulated translocation and increased susceptibility to endosomal ablation, These residues, together with other identified sequences within the C-terminus of Glut4, are likely to be crucial targeting elements that regulate Glut4 subcellular distribution. (C) 2000 Federation of European Biochemical Societies, Published by Elsevier Science B.V. All rights reserved.