Arginine-427 in the Na+/glucose cotransporter (SGLT1) is involved in trafficking to the plasma membrane

To investigate the role of charged intramembrane residues in the function of the rabbit Na+/glucose cotransporter (rbSGLT1) we substituted arginine-427 (R427) by alanine in the putative domain M9 SGLT1, This residue is conserved in all the members of the SGLT1 family. The mutant protein (R427A) was expressed in Xenopus oocytes and, although Western blot analysis revealed that it was produced in amounts comparable to wildtype, no function was measured. Freeze-fracture analysis showed that R427A SGLT1 was not in the plasma membrane while immunocytochemical experiments localized the transporter to just beneath it, These results indicate that arginine-427 plays a critical role in SGLT1 trafficking to the plasma membrane.