Reexamining the role of choline transporter-like (Ctlp) proteins in choline transport.
In Saccharomyces cerevisiae, choline enters the cell via a single high-affinity transporter, Hnmlp. hnm1delta cells lacking HNM1 gene are viable. However, they are unable to transport choline suggesting that no additional active choline transporters are present in this organism. A complementation study of a choline auxotrophic mutant, ctrl-ise (hnm1-ise), using a cDNA library from Torpedo marmorata electric lobe identified a membrane protein named Torpedo marmorata choline transporter-like, tCtl1p. tCtllp was proposed to mediate a high-affinity choline transport (O'Regan et al., 1999, Proc. Natl. Acad. Sci.). Homologs of tCtl1p have been identified in other organisms, including yeast (Pns1p, YOR161c) and are postulated to function as choline transporters. Here we provide several lines of evidence indicating that Ctlp proteins are not involved in choline transport. Loss of PNS1 has no effect on choline transport and overexpression of either PNS1 or tCTL1 does not restore choline uptake activity of choline transport-defective mutants. The data presented here call into question the role of proteins of the CTL family in choline transport and suggest that the mechanism by which tCTL1 complements hnm1-ise mutant is independent of its ability to transport choline.
Center for Microbial Pathogenesis, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, Connecticut, USA.
Rachel
R
Zufferey
Teresa C
TC
Santiago
Valerie
V
Brachet
Choukri
C
Ben Mamoun
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002794:Choline / Q000378:metabolism*; D018698:Glutamic Acid; D005998:Glycine; D007294:Inositol / Q000378:metabolism; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D014101:Torpedo
D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C484026:PNS1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C065637:choline transporter; D018698:Glutamic Acid; D007294:Inositol; D002794:Choline; D005998:Glycine