Conformational change in the mitochondrial channel, VDAC, detected by electron cryo-microscopy.

Crystalline arrays of the voltage-dependent channel, VDAC, can be produced by treatment of Neurospora mitochondrial outer membranes with phospholipase A2. The membrane crystals undergo a lateral phase transition (lattice contraction) that can be induced by an amphipathic polyanion, which also reduces the channel's gating potential. Electron cryo-microscopy of frozen-hydrated crystals indicates that the mean projected diameters of the channels do not decrease with lattice contraction. Instead, contraction is associated with the disappearance of lateral protein "arms" that normally extend between the channels. A model is presented that explains the changes in channel packing and gating potential in terms of a conformational change involving the movement of a protein "arm" between the bilayer and the channel.