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 funct ion of the rabbit Na+/glucose cotransporter (rbSGLT1) we substituted a rginine-427 (R427) by alanine in the putative domain M9 SGLT1, This re sidue 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 th at R427A SGLT1 was not in the plasma membrane while immunocytochemical experiments localized the transporter to just beneath it, These resul ts indicate that arginine-427 plays a critical role in SGLT1 trafficki ng to the plasma membrane.