Cystinosin, the protein defective in cystinosis, is a H(+)-driven lysosomal cystine transporter.
Cystinosis is an inherited lysosomal storage disease characterized by defective transport of cystine out of lysosomes. However, the causative gene, CTNS, encodes a seven transmembrane domain lysosomal protein, cystinosin, unrelated to known transporters. To investigate the molecular function of cystinosin, the protein was redirected from lysosomes to the plasma membrane by deletion of its C-terminal GYDQL sorting motif (cystinosin-DeltaGYDQL), thereby exposing the intralysosomal side of cystinosin to the extracellular medium. COS cells expressing cystinosin-DeltaGYDQL selectively take up L-cystine from the extracellular medium at acidic pH. Disruption of the transmembrane pH gradient or incubation of the cells at neutral pH strongly inhibits the uptake. Cystinosin-DeltaGYDQL is directly involved in the observed cystine transport, since this activity is highly reduced when the GYDQL motif is restored and is abolished upon introduction of a point mutation inducing early-onset cystinosis. We conclude that cystinosin represents a novel H(+)-driven transporter that is responsible for cystine export from lysosomes, and propose that cystinosin homologues, such as mammalian SL15/Lec35 and Saccharomyces cerevisiae ERS1, may perform similar transport processes at other cellular membranes.
Kalatzis
V
V
INSERM U423, Université René Descartes, Hôpital Necker-Enfants Malades, 149 rue de Sèvres, 75015 Paris, France.
Cherqui
S
S
Antignac
C
C
Gasnier
B
B
D020816:Amino Acid Motifs / Q000502:physiology; D026921:Amino Acid Transport Systems, Neutral; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003553:Cystine / Q000378:metabolism* / Q000493:pharmacokinetics; D003554:Cystinosis / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000378:metabolism*; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011522:Protons; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics; D013379:Substrate Specificity; D014162:Transfection
D026921:Amino Acid Transport Systems, Neutral; C111445:CTNS protein, human; D002352:Carrier Proteins; D006023:Glycoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011522:Protons; D011994:Recombinant Proteins; D003553:Cystine