Substrate specificity of a chimera made from Xenopus SGLT1-like protein and rabbit SGLT1.
To characterize the sugar translocation pathway of Na(+)/glucose cotransporter type 1 (SGLT1), a chimera was made by substituting the extracellular loop between transmembrane domain (TM) 12 and TM13 of Xenopus SGLT1-like protein (xSGLT1L) with the homologous region of rabbit SGLT1. The chimera was expressed in Xenopus oocytes and its transport activity was measured by the two-microelectrode voltage-clamp method. The substrate specificity of the chimera was different from those of xSGLT1L and SGLT1. In addition the chimera's apparent Michaelis-Menten constant (K(m)) for myo-inositol, 0.06 mM, was about one fourth of that of xSGLT1L, 0.25 mM, while the chimera's apparent K(m) for d-glucose, 0.8 mM, was about one eighth of that of xSGLT1L, 6.3 mM. Our results suggest that the extracellular loop between TM12 and TM13 participates in the sugar transport of SGLT1.
Nagata
Katsumi
K
Department of Biomedical Science, Institute of Regenerative Medicine and Biofunction, Tottori University Graduate School of Medical Science, Nishimachi 86, Yonago 683-8503, Japan. knag@grape.med.tottori-u.ac.jp
Hata
Yoshio
Y
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D008969:Molecular Sequence Data; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D051269:Sodium-Glucose Transporter 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity; D014981:Xenopus; D029867:Xenopus Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D017931:DNA Primers; C495673:SLC5A11 protein, Xenopus; D051269:Sodium-Glucose Transporter 1; D029867:Xenopus Proteins