Functional characterization of two novel mammalian electrogenic proton-dependent amino acid cotransporters.
We cloned two cDNAs encoding proton/amino acid cotransporters, designated as mPAT1 and mPAT2, from murine tissues. They were identified by sequence similarity to the amino acid/auxin permease family member of lower eukaryotes. We functionally characterized both transporters by flux studies and electrophysiology after expression in Xenopus laevis oocytes. Both mPAT1 and mPAT2 induced a pH-dependent electrogenic transport activity for small amino acids (glycine, alanine, and proline) that is altered by membrane potential. Direct evidence for amino acid/H(+)-symport was shown by intracellular acidification, and a flux coupling stoichiometry for proline/H(+)-symport of 1:1 was determined for both transporters. Besides small apolar L-amino acids, the transporters also recognize their D-enantiomers and selected amino acid derivatives such as gamma-aminobutyric acid. The mPAT1 transporter, the murine orthologue of the recently cloned rat LYAAT-1 transporter, can be considered as a low affinity system when compared with mPAT2. The mRNA of mPAT1 is highly expressed in small intestine, colon, kidney, and brain; the mPAT2-mRNA is mainly found in heart and lung. Phenotypically, the PAT1 transporter possesses the same functional characteristics as the previously described proton-dependent amino acid transport process in apical membranes of intestinal and renal epithelial cells.
Boll
Michael
M
Molecular Nutrition Unit, Institute of Nutritional Sciences, Technical University of Munich, D-85350 Freising-Weihenstephan, Germany.
Foltz
Martin
M
Rubio-Aliaga
Isabel
I
Kottra
Gabor
G
Daniel
Hannelore
H
D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004594:Electrophysiology; D004847:Epithelial Cells / Q000378:metabolism; D005998:Glycine / Q000737:chemistry; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions; D007700:Kinetics; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011392:Proline / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018075:RNA, Complementary / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D000076988:Sulfate Transporters; D027981:Symporters; D014018:Tissue Distribution; D014162:Transfection; D014982:Xenopus laevis
D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids; D002352:Carrier Proteins; D018076:DNA, Complementary; D007477:Ions; D008164:Luminescent Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D018075:RNA, Complementary; D012333:RNA, Messenger; C439529:SLC26A6 protein, human; C459819:Slc36a2 protein, mouse; D000076988:Sulfate Transporters; D027981:Symporters; D049452:Green Fluorescent Proteins; D011392:Proline; D000409:Alanine; D005998:Glycine