Lysosomal free-cystine

Lysosomal free-cystine refers to the accumulation of the amino acid dimer cystine within the lysosomes of cells. This phenomenon is most notably associated with cystinosis, a rare autosomal recessive disorder caused by mutations in the CTNS gene encoding cystinosin, which is responsible for transporting cystine out of lysosomes. When this transporter is defective, free-cystine accumulates, leading to crystal formation inside cells throughout various tissues. This disrupts cellular metabolism, oxidative balance, mitochondrial function, autophagy, and apoptosis. The buildup of lysosomal free-cystine underlies tissue damage seen in diseases like nephropathic Fanconi syndrome. Treatment strategies focus on reducing intralysosomal cystine using drugs such as cysteamine, which chemically modifies accumulated cystine so it can be exported from the lysosome and metabolized safely by the cell[1][2]. \n\nNote: \"Lysosomal free-cystine\" describes a small molecule metabolite within an organelle rather than a canonical therapeutic target such as an enzyme or receptor; thus it does not fit standard molecular classification schemes for drug targets or receptors. The actual therapeutic target relevant here would be \"Cystinosin\" (the transporter), not \"lysosomal free-cystine\" itself.\n\nThere may be confusion or incorrectness if \"Lysosomal free-cystine\" is listed as a druggable protein/receptor/target—this term refers instead to an abnormal metabolite accumulation due to transporter dysfunction.[1]

Other names

Lysosomal cystineFree cystine in lysosomeIntracellular cystine (lysosomal)

Cysteamine reacts with lysosomal cystine to form a mixed disulfide that can exit the lysosome, reducing toxic accumulation of free-cystine in cells[1].