Hereditary folate malabsorption due to a mutation in the external gate of the proton-coupled folate transporter SLC46A1

Srinivas Aluri, Rongbao Zhao, Charlotte Lubout, Susanna M.I. Goorden, Andras Fiser, I. David Goldman

Research output: Contribution to journalArticle

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Abstract

Hereditary folate malabsorption (HFM) is an autosomal recessive disorder characterized by impaired intestinal folate absorption and impaired folate transport across the choroid plexus due to loss of function of the proton-coupled folate transporter (PCFT-SLC46A1). We report a novel mutation, causing HFM, affecting a residue located in the 11th transmembrane helix within the external gate. The mutant N411K-PCFT was stable, trafficked to the cell membrane, and had sufficient residual activity to characterize the transport defect and the structural requirements at this site for gate function. The influx Vmax of the N411K mutant was markedly decreased, as was the affinity for most, but not all, folate/antifolate substrates. The greatest loss of activity was for 5-methyltetrahydrofolate. Substitutions with positive charged residues resulted in a loss of activity (arginine > lysine > histidine). Function was retained for the negative charged aspartate, but not the larger glutamate substitutions, whereas the bulky hydrophobic (leucine), or polar (glutamine) substitutions, were tolerated. Homology models of PCFT, in the inward and outward open conformations, based upon the mammalian Glut5 fructose transporter structures, localize Asn411 protruding into the aqueous pathway. This is most prominent when the carrier is in the inward open conformation when the external gate is closed. Mutations at this site likely result in highly specific steric and electrostatic interactions between the Asn411-substituted, and other, residues in the gate region that impede carrier function. The substrate specificity of the N411K mutant may be due to alterations of substrate flows through the external gate, downstream allosteric alterations in the folate-binding pocket, or both.

Original languageEnglish (US)
Pages (from-to)61-68
Number of pages8
JournalBlood advances
Volume2
Issue number1
DOIs
StatePublished - Jan 9 2018

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Proton-Coupled Folate Transporter
Folic Acid
Mutation
Folic Acid Antagonists
Choroid Plexus
Intestinal Absorption
Substrate Specificity
Fructose
Glutamine
Static Electricity
Histidine
Aspartic Acid
Leucine
Lysine
Arginine
Glutamic Acid
Cell Membrane
Hereditary Folate Malabsorption

ASJC Scopus subject areas

  • Medicine(all)

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Hereditary folate malabsorption due to a mutation in the external gate of the proton-coupled folate transporter SLC46A1. / Aluri, Srinivas; Zhao, Rongbao; Lubout, Charlotte; Goorden, Susanna M.I.; Fiser, Andras; Goldman, I. David.

In: Blood advances, Vol. 2, No. 1, 09.01.2018, p. 61-68.

Research output: Contribution to journalArticle

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