title: N-linked glycosylation and its impact on the electrophoretic mobility and function of the human proton-coupled folate transporter (HsPCFT).
abstract: The human proton-coupled folate transporter (HsPCFT, SLC46A1) mediates intestinal absorption of folates and transport of folates into the liver, brain and other tissues. On Western blot, HsPCFT migrates as a broad band (~55 kDa), higher than predicted (~50 kDa) in cell lines. Western blot analysis required that membrane preparations not be incubated in the loading buffer above 50 degrees C to avoid aggregation of the protein. Treatment of membrane fractions from HsPCFT-transfected HeLa cells with peptidyl N-glycanase F, or cells with tunicamycin, resulted in conversion to a ~35 kDa species. Substitution of asparagine residues of two canonical glycosylation sites to glutamine, individually, yielded a ~47 kDa protein; substitution of both sites gave a smaller (~35 kDa) protein. Single mutants retained full transport activity; the double mutant retained a majority of activity. Transport function and molecular size were unchanged when the double mutant was hemagglutinin (HA) tagged at either the NH(2) or COOH terminus and probed with an anti-HA antibody excluding degradation of the deglycosylated protein. Wild-type or deglycosylated HsPCFT HA, tagged at amino or carboxyl termini, could only be visualized on the plasma membrane when HeLa cells were first permeabilized, consistent with the intracellular location of these domains.
authors.affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Ersin Selcuk
authors.initials: ES
authors.lastname: Unal
authors.forename: Rongbao
authors.initials: R
authors.lastname: Zhao
authors.forename: Andong
authors.initials: A
authors.lastname: Qiu
authors.forename: I David
authors.initials: ID
authors.lastname: Goldman
mesh_terms: D019943:Amino Acid Substitution; D001693:Biological Transport, Active / Q000502:physiology; D015153:Blotting, Western; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000378:metabolism; D006031:Glycosylation; D006367:HeLa Cells; D006801:Humans; D007408:Intestinal Absorption / Q000502:physiology; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008970:Molecular Weight; D020125:Mutation, Missense; D058979:Proton-Coupled Folate Transporter; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D026901:Membrane Transport Proteins; D058979:Proton-Coupled Folate Transporter; D011956:Receptors, Cell Surface; C505058:SLC46A1 protein, human; D005492:Folic Acid