Aromatic amino acid transporter AAT-9 of Caenorhabditis elegans localizes to neurons and muscle cells.
The Caenorhabditis elegans genome encodes nine homologues of mammalian glycoprotein-associated amino acid transporters. Two of these C. elegans proteins (AAT-1 and AAT-3) have been shown to function as catalytic subunits (light chains) of heteromeric amino acid transporters. These proteins need to associate with a glycoprotein heavy chain subunit (ATG-2) to reach the cell surface in a manner similar to that of their mammalian homologues. AAT-1 and AAT-3 contain a cysteine residue in the second putative extracellular loop through which a disulfide bridge can form with a heavy chain. In contrast, six C. elegans members of this family (AAT-4 to AAT-9) lack such a cysteine residue. We show here that one of these transporter proteins, AAT-9, reaches the cell surface in Xenopus oocytes without an exogenous heavy chain and that it functions as an exchanger of aromatic amino acids. Two-electrode voltage clamp experiments demonstrate that AAT-9 displays a substrate-activated conductance. Immunofluorescence shows that it is expressed close to the pharyngeal bulbs within C. elegans neurons. The selective expression of an aat-9 promoter-green fluorescent protein construct in several neurons of this region and in wall muscle cells around the mouth supports and extends these localization data. Taken together, the results show that AAT-9 is expressed in excitable cells of the nematode head and pharynx in which it may provide a pathway for aromatic amino acid transport.
Veljkovic
Emilija
E
Institutes of Physiology and Zoology, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
Bacconi
Andrea
A
Stetak
Attila
A
Hajnal
Alex
A
Stasiuk
Susan
S
Skelly
Patrick J
PJ
Forster
Ian
I
Shoemaker
Charles B
CB
Verrey
Francois
F
D026905:Amino Acid Transport Systems / Q000096:biosynthesis* / Q000737:chemistry* / Q000235:genetics; D024322:Amino Acids, Aromatic / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D017173:Caenorhabditis elegans; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D003545:Cysteine / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D004220:Disulfides; D004594:Electrophysiology; D020868:Gene Silencing; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007477:Ions; D007700:Kinetics; D007980:Levodopa / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009132:Muscles / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D010641:Phenotype; D010649:Phenylalanine / Q000737:chemistry; D010802:Phylogeny; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D018075:RNA, Complementary / Q000378:metabolism; D013997:Time Factors; D019076:Transgenes; D014982:Xenopus laevis
C494776:AAT-9 protein, C elegans; D026905:Amino Acid Transport Systems; D024322:Amino Acids, Aromatic; D018076:DNA, Complementary; D004220:Disulfides; D007477:Ions; D018075:RNA, Complementary; D049452:Green Fluorescent Proteins; D007980:Levodopa; D010649:Phenylalanine; D003545:Cysteine