A novel loss-of-function mutation in the proton-coupled folate transporter from a patient with hereditary folate malabsorption reveals that Arg 113 is crucial for function

Blood. 2008 Sep 1;112(5):2055-61. doi: 10.1182/blood-2008-04-150276. Epub 2008 Jun 17.


Hereditary folate malabsorption (HFM) patients harbor inactivating mutations including R113S in the proton-coupled folate transporter (PCFT), an intestinal folate transporter with optimal activity at acidic pH. Here we identified and characterized a novel R113C mutation residing in the highly conserved first intracellular loop of PCFT. Stable transfectants overexpressing a Myc-tagged wild-type (WT) and mutant R113C PCFT displayed similar transporter targeting to the plasma membrane. However, whereas WT PCFT transfectants showed a 22-fold increase in [(3)H]folic acid influx at pH 5.5, R113C or mock transfectants showed no increase. Moreover, WT PCFT transfectants displayed a 50% folic acid growth requirement concentration of 7 nM, whereas mock and R113C transfectants revealed 24- to 27-fold higher values. Consistently, upon fluorescein-methotrexate labeling, WT PCFT transfectants displayed a 50% methotrexate displacement concentration of 50 nM, whereas mock and R113C transfectants exhibited 12- to 14-fold higher values. Based on the crystal structure of the homologous Escherichia coli glycerol-3-phosphate transporter, we propose that the cationic R113 residue of PCFT is embedded in a hydrophobic pocket formed by several transmembrane helices that may be part of a folate translocation pore. These findings establish a novel loss of function mutation in HFM residing in an intracellular loop of PCFT crucial for folate transport.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Arginine / chemistry
  • Base Sequence
  • Binding Sites / genetics
  • CHO Cells
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism
  • Cell Membrane / metabolism
  • Child
  • Consanguinity
  • Cricetinae
  • Cricetulus
  • DNA Primers / genetics
  • Folate Receptors, GPI-Anchored
  • Folic Acid / metabolism*
  • Homozygote
  • Humans
  • Hydrogen-Ion Concentration
  • In Vitro Techniques
  • Malabsorption Syndromes / genetics*
  • Malabsorption Syndromes / metabolism*
  • Methotrexate / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Point Mutation*
  • Protein Conformation
  • Receptors, Cell Surface / chemistry
  • Receptors, Cell Surface / deficiency
  • Receptors, Cell Surface / genetics*
  • Receptors, Cell Surface / metabolism
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Transfection


  • Carrier Proteins
  • DNA Primers
  • Folate Receptors, GPI-Anchored
  • Receptors, Cell Surface
  • Recombinant Proteins
  • Folic Acid
  • Arginine
  • Methotrexate