title: Hereditary folate malabsorption: a positively charged amino acid at position 113 of the proton-coupled folate transporter (PCFT/SLC46A1) is required for folic acid binding.
abstract: The proton-coupled folate transporter (PCFT/SLC46A1) mediates intestinal folate uptake at acidic pH. Some loss of folic acid (FA) transport mutations in PCFT from hereditary folate malabsorption (HFM) patients cluster in R113, thereby suggesting a functional role for this residue. Herein, unlike non-conservative substitutions, an R113H mutant displayed 80-fold increase in the FA transport Km while retaining parental Vmax, hence indicating a major fall in folate substrate affinity. Furthermore, consistent with the preservation of 9% of parental transport activity, R113H transfectants displayed a substantial decrease in the FA growth requirement relative to mock transfectants. Homology modeling based on the crystal structures of the Escherichia coli transporter homologues EmrD and glycerol-3-phosphate transporter revealed that the R113H rotamer properly protrudes into the cytoplasmic face of the minor cleft normally occupied by R113. These findings constitute the first demonstration that a basic amino acid at position 113 is required for folate substrate binding.
authors.affiliation: The Fred Wyszkowski Cancer Research Laboratory, Dept. of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Inbal
authors.initials: I
authors.lastname: Lasry
authors.forename: Bluma
authors.initials: B
authors.lastname: Berman
authors.forename: Fabian
authors.initials: F
authors.lastname: Glaser
authors.forename: Gerrit
authors.initials: G
authors.lastname: Jansen
authors.forename: Yehuda G
authors.initials: YG
authors.lastname: Assaraf
mesh_terms: D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005492:Folic Acid / Q000378:metabolism*; D006801:Humans; D007408:Intestinal Absorption / Q000235:genetics*; D008286:Malabsorption Syndromes / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D058979:Proton-Coupled Folate Transporter
chemical_list: D026901:Membrane Transport Proteins; D058979:Proton-Coupled Folate Transporter; C505058:SLC46A1 protein, human; D005492:Folic Acid; D001120:Arginine