Structure and function of mitochondrial carriers - role of the transmembrane helix P and G residues in the gating and transport mechanism.

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.