The Mitochondrial Porins

The mitochondrial outer membrane contains a permeability channel that is responsible for the passage of hydrophilic compounds across the membrane. The transmembrane protein, called mitochondrial porin is not particularly hydrophobic and its primary structure does not contain any indication for the existence of transmembrane hydrophobic α-helical structures typical for membrane channels from the nerve and muscle tissues. Instead, it contains a strong indication for the existence of β-strands that are typical for the secondary structure of bacterial porins. The mitochondrial porin forms voltage-gated channels in artificial lipid bilayer membranes. The open channel has a small preference for anion over cations of the same aqueous mobility. The ion-permeable closed state is cation-selective and is impermeable for ATP and ADP.