Reanalysis of structure/function correlations in the region of transmembrane segments 4 and 5 of the rabbit sodium/glucose cotransporter.
The predicted topology of the mammalian high-affinity sodium/glucose cotransporter (SGLT1), in the region surrounding transmembrane segments 4 and 5, disagrees with the recent published crystal structure of bacterial SGLT from Vibrio parahaemolyticus (vSGLT). To investigate this issue further, 38 residues from I143 to A180 in the N-terminal half of rabbit SGLT1 were each replaced with cysteine and then expressed in COS-7 cells or Xenopus laevis oocytes. The membrane orientations of the substituted cysteines were determined by treatment with the thiol-specific reagent N-Biotinoylaminoethyl methanethiosulfonate (biotin-MTSEA), combined with the membrane impermeant thiol-specific reagent sodium (2-sulfonatoethyl) methanethiosulfonate (MTSES). The present results combined with previous structure/function studies of SGLT1, suggest that transmembrane domain (TM) 4 of mammalian SGLT1 extends from residue 143-171 and support the topology observed in the crystal structure of vSGLT.
Liu
Tiemin
T
Department of Medicine, University of Toronto, Medical Sciences Building, Room 7336, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8.
Speight
Pam
P
Silverman
Mel
M
D000595:Amino Acid Sequence; D000818:Animals; D019921:Biotinylation / Q000235:genetics; D019556:COS Cells; D002462:Cell Membrane; D002522:Chlorocebus aethiops; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011817:Rabbits; D051269:Sodium-Glucose Transporter 1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
D051269:Sodium-Glucose Transporter 1; D003545:Cysteine