Identification and characterization of a lysosomal transporter for small neutral amino acids.
In eukaryotic cells, lysosomes represent a major site for macromolecule degradation. Hydrolysis products are eventually exported from this acidic organelle into the cytosol through specific transporters. Impairment of this process at either the hydrolysis or the efflux step is responsible of several lysosomal storage diseases. However, most lysosomal transporters, although biochemically characterized, remain unknown at the molecular level. In this study, we report the molecular and functional characterization of a lysosomal amino acid transporter (LYAAT-1), remotely related to a family of H+-coupled plasma membrane and synaptic vesicle amino acid transporters. LYAAT-1 is expressed in most rat tissues, with highest levels in the brain where it is present in neurons. Upon overexpression in COS-7 cells, the recombinant protein mediates the accumulation of neutral amino acids, such as gamma-aminobutyric acid, l-alanine, and l-proline, through an H+/amino acid symport. Confocal microscopy on brain sections revealed that this transporter colocalizes with cathepsin D, an established lysosomal marker. LYAAT-1 thus appears as a lysosomal transporter that actively exports neutral amino acids from lysosomes by chemiosmotic coupling to the H+-ATPase of these organelles. Homology searching in eukaryotic genomes suggests that LYAAT-1 defines a subgroup of lysosomal transporters in the amino acid/auxin permease family.
Sagné
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C
Institut National de la Santé et de la Recherche Médicale U-513, CHU Henri Mondor, 8 Rue du Général Sarrail, 94010 Créteil Cedex, France. sagne@im3.inserm.fr
Agulhon
C
C
Ravassard
P
P
Darmon
M
M
Hamon
M
M
El Mestikawy
S
S
Gasnier
B
B
Giros
B
B
D000409:Alanine / Q000378:metabolism; D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; D021542:Amino Acids, Neutral / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism*; D017173:Caenorhabditis elegans; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D002540:Cerebral Cortex / Q000378:metabolism; D003001:Cloning, Molecular; D004331:Drosophila melanogaster; D019143:Evolution, Molecular; D006624:Hippocampus / Q000378:metabolism; D007700:Kinetics; D008247:Lysosomes / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D010802:Phylogeny; D011392:Proline / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D027981:Symporters; D014162:Transfection; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; D021542:Amino Acids, Neutral; D002352:Carrier Proteins; D011994:Recombinant Proteins; C493537:Slc36a1 protein, rat; D027981:Symporters; D005680:gamma-Aminobutyric Acid; D011392:Proline; D000409:Alanine