Glucose transporter glycosylation

K. Ohtsubo, S. Takamatsu, M. T. Minowa, A. Yoshida, M. Takeuchi, and J. D. Marth, Dietary and genetic control of glucose transporter 2 glycosylation promotes insulin secretion in suppressing diabetes, Cell, 123 (2005) 1307-1321. 

Figure 1. Models for the orientation of A.) Members of the facilitative glucose transporter family (CLUT1 to GLUT7), and B.) the sodium-dependent glucose transporter (SGLT1). The branched structure is at the site of glycosylation for both transporters. In A, the open residues represent amino acids which are identical in GLUT1 through GLUT5.

Glycosylation has also been reported to improve intestinal absorption of peptide drugs which demonstrate poor membrane penetrability. For instance, glycosylation at the /V-terminus of tetrapeptide (Gly-Gly-Tyr-Arg) increases its resistance to degradation by peptidases in addition, Na+-dependent glucose transporters were shown to play an important role in the intestinal absorption of both /)-(succinylamido)phenyl a- or p-D-ghicopyranosides (Nomoto et al. 1998). 

G. Muller, E.A. Dearey, A. Korndor-EER, and W. Bandlow, Stimulation of a glycosyl-phosphatidylinositol-specific phospholipase by insulin and the sulfonylurea, glimepiride, in rat adipocytes depends on increased glucose transport, J. Cell. Biol., 1994, 126, 1267-1276. 

A notable finding was the defective transport of D-glucose, uridine, and two amino acid analogs (2-aminobutanoate and cycloleucine) in chick-embryo cells in which glycosylation of proteins was prevented by tunicamycin. Other membrane-associated processes, such as the enzymic activities of Na/K ATPase and adenylate cyclase, or the stimulation of adenylate cyclase by a prostaglandin and cholerae toxin, were not affected.546... 

---