Functional roles of aspartate residues of the proton-coupled folate transporter (PCFT-SLC46A1); a D156Y mutation causing hereditary folate malabsorption.
The proton-coupled folate transporter (PCFT; SLC46A1) mediates folate transport into enterocytes in the proximal small intestine; pcft loss-of-function mutations are the basis for hereditary folate malabsorption. The current study explored the roles of Asp residues in PCFT function. A novel, homozygous, loss-of-function mutation, D156Y, was identified in a child of Pakistani origin with hereditary folate malabsorption. Of the 6 other conserved Asp residues, only one, D109, is shown to be required for function. D156Y, along with a variety of other substitutions at this site (Trp, Phe, Val, Asn, or Lys), lacked function due to instability of the PCFT protein. Substantial function was preserved with Glu, Gly, and, to a lesser extent, with Ser, Thr, and Ala substitutions. This correlated with PCFT bio-tinylated at the cell surface. In contrast, all D109 mutants, including D109E, lacked function irrespective of pH (4.5, 5.5, and 7.4) or substrate concentration (0.5-100 μM), despite surface expression comparable to wild-type PCFT. Hence, D156 plays a critical role in PCFT protein stability, and D109, located in the first intracellular loop between the second and third transmembrane domains, is absolutely required for PCFT function.
Shin
Daniel Sanghoon
DS
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY, USA.
Min
Sang Hee
SH
Russell
Laura
L
Zhao
Rongbao
R
Fiser
Andras
A
Goldman
I David
ID
D019943:Amino Acid Substitution; D001224:Aspartic Acid; D002648:Child; D004252:DNA Mutational Analysis; D005492:Folic Acid / Q000378:metabolism; D006720:Homozygote; D006801:Humans; D007231:Infant, Newborn; D008286:Malabsorption Syndromes / Q000235:genetics*; D020125:Mutation, Missense; D010154:Pakistan; D055550:Protein Stability; D058979:Proton-Coupled Folate Transporter / Q000235:genetics*
D058979:Proton-Coupled Folate Transporter; D001224:Aspartic Acid; D005492:Folic Acid
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