SLC66A1 (also known as PQLC2) is a lysosomal transmembrane transporter that specifically mediates the pH-dependent export of cationic amino acids arginine, lysine, and histidine from lysosomes 1. The protein localizes to the lysosomal membrane and catalyzes robust, electrogenic transport that is selective for cationic amino acids and strongly activated at low extracytosolic pH 1. Beyond its transport function, SLC66A1 serves as a nutrient sensor that recruits the C9orf72-SMCR8-WDR41 protein complex to lysosomes in response to cationic amino acid starvation 2. This recruitment occurs through a direct interaction between SLC66A1 and WDR41, which is negatively regulated by the availability of arginine, lysine, and histidine 2. The transporter functions as a transceptor, where conformational changes related to substrate transport regulate the availability of the WDR41-binding site 3. Clinically, biallelic deletions in SLC66A1 have been identified as a novel cause of autosomal recessive rod-cone dystrophy and retinitis pigmentosa 45. The protein also plays a role in cysteamine therapy for cystinosis by transporting lysine-like mixed disulfides that serve as chemical intermediates in treatment 1.