title: The endogenous CXXC motif governs the cadmium sensitivity of the renal Na+/glucose co-transporter.
abstract: Cadmium (Cd2+) poisoning causes severe renal disorders manifested by defects in reabsorptive transport of various compounds. It is reported here that the renal brush-border membrane Na+/glucose co-transporter-1 (SGLT1) is a molecular target for Cd2+ toxicity. In micromolar concentrations, Cd2+ acted as a noncompetitive, partial inhibitor of methyl-D-glucopyranoside uptake in vesicles from COS-7 cells transiently expressing SGLT1. In contrast, only a modest effect in the closely related Na+/myo-inositol co-transporter-1 (SMIT1) was observed. The factor responsible for this difference was the CXXC motif (X can be any residue) at the cytoplasmic end of the eighth transmembrane segment (TM8) of SGLT1. Thus, a mutational transfer of this motif conveyed Cd2+ sensitivity to SMIT1. Moreover, mimicking the inhibitory effect of Cd2+, the biarsenical molecule FlAsH-EDT2 strongly inhibited the SGLT1 that had an engineered tetracysteine motif at the cytoplasmic end of TM8. The experiments also showed that covalent binding of the sulfhydryl reactive biotin-PEO-maleimide to the SGLT1 wild type but not to the mutant lacking the CXXC motif was suppressed by Cd2+. Taken together, these results suggest that in SGLT1, Cd2+ binding to the CXXC motif induces conformational changes that cause a partial inhibition of d-glucose transport.
authors.affiliation: Beijing 302 Hospital, Beijing, People's Republic of China 100039. xiaobingmpi@yahoo.com
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Xia
authors.forename: Gang
authors.initials: G
authors.lastname: Wang
authors.forename: Yanchun
authors.initials: Y
authors.lastname: Peng
authors.forename: Ming-Gene
authors.initials: MG
authors.lastname: Tu
authors.forename: Jimmy
authors.initials: J
authors.lastname: Jen
authors.forename: Hongqing
authors.initials: H
authors.lastname: Fang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D019556:COS Cells; D002104:Cadmium / Q000633:toxicity*; D002522:Chlorocebus aethiops; D003510:Cyclohexanes / Q000494:pharmacology; D003545:Cysteine / Q000737:chemistry; D007476:Ionophores / Q000494:pharmacology; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D008024:Ligands; D008051:Lipid Bilayers / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D008757:Methylglucosides / Q000493:pharmacokinetics; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051381:Rats; D051269:Sodium-Glucose Transporter 1
chemical_list: D003510:Cyclohexanes; D007476:Ionophores; D008024:Ligands; D008051:Lipid Bilayers; D008562:Membrane Glycoproteins; D008757:Methylglucosides; D009004:Monosaccharide Transport Proteins; C495676:Slc5a1 protein, rat; D051269:Sodium-Glucose Transporter 1; D002104:Cadmium; C027020:methylglucoside; C077946:N,N,N',N'-tetracyclohexyl-3-oxapentanediamide; D003545:Cysteine