Fig. 14. Various alternative (incorrect) schemes by which the VDAC channel might close. In the upper figure, a domain extends into the channel opening or into the channel proper. In the middle scheme, the b -strands are tilted in the open state and the tilt is reduced in the closed state producing a longer channel with narrower diameter. In the bottom figure, the channel is shown in cross-section. Closure here results from either the partial collapse of the cylinder or the overlap of the free ends of the cylinder.