A single amino acid change converts the sugar sensor SGLT3 into a sugar transporter

Laura Bianchi, Ana Díez-Sampedro

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

Background: Sodium-glucose cotransporter proteins (SGLT) belong to the SLC5A family, characterized by the cotransport of Na+ with solute. SGLT1 is responsible for intestinal glucose absorption. Until recently the only role described for SGLT proteins was to transport sugar with Na+. However, human SGLT3 (hSGLT3) does not transport sugar but causes depolarization of the plasma membrane when expressed in Xenopus oocytes. For this reason SGLT3 was suggested to be a sugar sensor rather than a transporter. Despite 70% amino acid identity between hSGLT3 and hSGLT1, their sugar transport, apparent sugar affinities, and sugar specificity differ greatly. Residue 457 is important for the function of SGLT1 and mutation at this position in hSGLT1 causes glucose-galactose malabsorption. Moreover, the crystal structure of vibrio SGLT reveals that the residue corresponding to 457 interacts directly with the sugar molecule. We thus wondered if this residue could account for some of the functional differences between SGLT1 and SGLT3. Methodology/Principal Findings: We mutated the glutamate at position 457 in hSGLT3 to glutamine, the amino acid present in all SGLT1 proteins, and characterized the mutant. Surprisingly, we found that E457Q-hSGLT3 transported sugar, had the same stoichiometry as SGLT1, and that the sugar specificity and apparent affinities for most sugars were similar to hSGLT1. We also show that SGLT3 functions as a sugar sensor in a living organism. We expressed hSGLT3 and E457Q-hSGLT3 in C. elegans sensory neurons and found that animals sensed glucose in an hSGLT3-dependent manner. Conclusions/Significance: In summary, we demonstrate that hSGLT3 functions as a sugar sensor in vivo and that mutating a single amino acid converts this sugar sensor into a sugar transporter similar to SGLT1. Copyright:

Original languageEnglish
Article numbere10241
JournalPLoS One
Volume5
Issue number4
DOIs
StatePublished - Sep 10 2010

Fingerprint

Sugars
transporters
sugars
Amino Acids
amino acids
Sodium-Glucose Transport Proteins
Sensors
Sodium-Glucose Transporter 1
glucose
Glucose
Vibrio
Intestinal Absorption
Sensory Receptor Cells
Xenopus
Glutamine
Oocytes
Glutamic Acid
Cell Membrane
malabsorption
proteins

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Medicine(all)

Cite this

A single amino acid change converts the sugar sensor SGLT3 into a sugar transporter. / Bianchi, Laura; Díez-Sampedro, Ana.

In: PLoS One, Vol. 5, No. 4, e10241, 10.09.2010.

Research output: Contribution to journalArticle

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abstract = "Background: Sodium-glucose cotransporter proteins (SGLT) belong to the SLC5A family, characterized by the cotransport of Na+ with solute. SGLT1 is responsible for intestinal glucose absorption. Until recently the only role described for SGLT proteins was to transport sugar with Na+. However, human SGLT3 (hSGLT3) does not transport sugar but causes depolarization of the plasma membrane when expressed in Xenopus oocytes. For this reason SGLT3 was suggested to be a sugar sensor rather than a transporter. Despite 70{\%} amino acid identity between hSGLT3 and hSGLT1, their sugar transport, apparent sugar affinities, and sugar specificity differ greatly. Residue 457 is important for the function of SGLT1 and mutation at this position in hSGLT1 causes glucose-galactose malabsorption. Moreover, the crystal structure of vibrio SGLT reveals that the residue corresponding to 457 interacts directly with the sugar molecule. We thus wondered if this residue could account for some of the functional differences between SGLT1 and SGLT3. Methodology/Principal Findings: We mutated the glutamate at position 457 in hSGLT3 to glutamine, the amino acid present in all SGLT1 proteins, and characterized the mutant. Surprisingly, we found that E457Q-hSGLT3 transported sugar, had the same stoichiometry as SGLT1, and that the sugar specificity and apparent affinities for most sugars were similar to hSGLT1. We also show that SGLT3 functions as a sugar sensor in a living organism. We expressed hSGLT3 and E457Q-hSGLT3 in C. elegans sensory neurons and found that animals sensed glucose in an hSGLT3-dependent manner. Conclusions/Significance: In summary, we demonstrate that hSGLT3 functions as a sugar sensor in vivo and that mutating a single amino acid converts this sugar sensor into a sugar transporter similar to SGLT1. Copyright:",
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