Fig. 1: Functional characterisation and structure determination of cystinosin.

a Cystinosin resides within the lysosomal membrane where it is responsible for the export of cystine from the lysosomal lumen. Transport is proton coupled, utilising the proton gradient across the membrane generated through the action of V-ATPase. Mutation of the CTNS gene, which encodes cystinosin, lead to cystinosis. b Representative K_M curve derived from TEVC for full length human cystinosin (WT – black) and a construct lacking N-terminal amino acids 2-115 (ΔN – blue). n = 16 independent experiments for every WT data point, n = 10 for ΔN, error bars SEM. K_M values were calculated from three biologically independent experiments, error SD. c Representative K_M analysis of plant cystinosin derived using a pyranine based in vitro assay. K_M was calculated from three independent experiments, error SD. Inset shows a typical set of raw data generated from the assay (lines are coloured according to cystine concentration dark green 800 via lighter colours to dark blue 0 μM). d Crystal structure of plant cystinosin with helices coloured blue to red from the N-terminus. Highlighted (magenta spheres) are the two PQ loop motifs which sit in the open cavity facing the cytoplasm in the conformation captured in the structure. e View of cystinosin highlighting the salt bridge network which forms the luminal lock and seals the binding site on the luminal side. Source data are provided as a Source Data file.