Expression cloning and cDNA sequencing of the Na+/glucose co-transporter |
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Authors: | M A Hediger M J Coady T S Ikeda E M Wright |
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Affiliation: | Department of Physiology, School of Medicine, University of California, Los Angeles 90024-1751. |
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Abstract: | Organic substrates (sugars, amino acids, carboxylic acids and neutrotransmitters) are actively transported into eukaryotic cells by Na+ co-transport. Some of the transport proteins have been identified--for example, intestinal brush border Na+/glucose and Na+/proline transporters and the brain Na+/CI-/GABA transporter--and progress has been made in locating their active sites and probing their conformational states. The archetypical Na+-driven transporter is the intestinal brush border Na+/glucose co-transporter (see ref. 8), and a defect in the co-transporter is the origin of the congenital glucose-galactose malabsorption syndrome. Here we describe cloning of this co-transporter by a method new to membrane proteins. We have sequenced the cloned DNA and have found no homology between the Na+/glucose co-transporter and either the mammalian facilitated glucose carrier or the bacterial sugar transport proteins. This suggests that the mammalian Na+-driven transporter has no evolutionary relationship to the other sugar transporters. |
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