Referenced in: none

Automatically associated channels: Slo1

Title: Mechanism of proton/substrate coupling in the heptahelical lysosomal transporter cystinosin.

Authors: Raquel Ruivo, Gian Carlo Bellenchi, Xiong Chen, Giovanni Zifarelli, Corinne Sagné, Cécile Debacker, Michael Pusch, Stéphane Supplisson, Bruno Gasnier

Journal, date & volume: , 2012 Jan 9 , ,

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/22232659

Abstract
Secondary active transporters use electrochemical gradients provided by primary ion pumps to translocate metabolites or drugs "uphill" across membranes. Here we report the ion-coupling mechanism of cystinosin, an unusual eukaryotic, proton-driven transporter distantly related to the proton pump bacteriorhodopsin. In humans, cystinosin exports the proteolysis-derived dimeric amino acid cystine from lysosomes and is impaired in cystinosis. Using voltage-dependence analysis of steady-state and transient currents elicited by cystine and neutralization-scanning mutagenesis of conserved protonatable residues, we show that cystine binding is coupled to protonation of a clinically relevant aspartate buried in the membrane. Deuterium isotope substitution experiments are consistent with an access of this aspartate from the lysosomal lumen through a deep proton channel. This aspartate lies in one of the two PQ-loop motifs shared by cystinosin with a set of eukaryotic membrane proteins of unknown function and is conserved in about half of them, thus suggesting that other PQ-loop proteins may translocate protons.