Cystine/H(+) symporter that mediates export of cystine, the oxidized dimer of cysteine, from lysosomes (PubMed:12370309). Plays an important role in melanin synthesis by catalyzing cystine export from melanosomes, possibly by inhibiting pheomelanin synthesis (PubMed:22649030). In addition to cystine export, also acts as a positive regulator of mTORC1 signaling in kidney proximal tubular cells, via interactions with components of the v-ATPase and Ragulator complexes (PubMed:26449607). Also involved in small GTPase-regulated vesicle trafficking and lysosomal localization of LAMP2A, independently of cystine transporter activity (PubMed:28465352). H(+)(out) + L-cystine(out) = H(+)(in) + L-cystine(in) Interacts with components of the V-ATPase complex (PubMed:26449607). Interacts with components of the Ragulator complex (PubMed:26449607). Interacts with RRAGA/RagA and RRAGC/RagC (PubMed:26449607). Interacts with AP-3 complex subunit mu (AP3M1 or AP3M2) (By similarity). AP-3 complex is required for localization to the lysosome. The lysosomal targeting motif, together with te second PQ-loop mediate targeting to the lysosome. Mice develop ocular damages, bone defects and behavioral anomalies (PubMed:12370309). Defects are caused by cystine accumulation in all organs tested, and formation of cystine crystals (PubMed:12370309). Mice do not develop signs of a proximal tubulopathy or renal failure (PubMed:12370309). Cystine accumulation in the central nervous system causes severe age-related memory deficits: spatial reference and working memory deficits are observed in middle-aged mice (PubMed:17977621). In eyes, cystine crystals induce inflammatory and immune response with aging associated with loss of keratocyte and endothelial cells (PubMed:21897743). Mice show a strong increase in hair pheomelanin content (PubMed:22649030). Decreased mTORC1 signaling pathway in proximal tubular cell lines (PubMed:26449607). Belongs to the cystinosin family.