Lysosomal transporters for cystine and related compounds

Intralysosomal cystine is formed by protein catabolism in the lysosome and is normally exported by a cystine transporter that contains a membrane protein, cystinosin (encoded by CTNS). Defects of this protein cause lysosomal accumulation of cystine.

Cysteamine enters the lysosome and combines with cystine to form cysteine (also known as half-cystine), which can be exported by the cysteine transporter, and cysteine-cysteamine, a mixed disulfide, which can be exported by the lysine transporter due to its structural analogy.