To date, 22 mitochondrial carrier subfamilies have been functionally identified based on substrate specificity. Structural, functional and bioinformatics studies have pointed to the existence in the mitochondrial carrier superfamily of a substrate-binding site in the internal carrier cavity, of two salt-bridge networks or gates that close the cavity alternatively on the matrix or the cytosolic side of the membrane, and of conserved prolines and glycines in the transmembrane alpha-helices. The significance of these properties in the structural changes occurring during the catalytic substrate translocation cycle are discussed within the context of a transport mechanism model. Most experimentally produced and disease-causing missense mutations concern carrier regions corresponding to the substrate-binding site, the two gates and the conserved prolines and glycines.
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