Structural and functional evidence for multiple channel complexes in the outer membrane of Neurospora crassa mitochondria.

The outer membrane of mitochondria contains proteins that form channels called VDAC (voltage-dependent anion-selective channels). Two independent lines of evidence suggest that these channels occur in specific complexes in the outer membrane of Neurospora mitochondria. Electron microscopic images of these outer membranes reveal polymorphic crystalline arrays of putative pores. These arrays can be shown to be interrelated by movement in the membrane plane of a particular rigid channel triplet or of regular aggregates of this triplet. Detergent extracts of the same outer membranes induce single- and multiple-step conductances in planar phospholipid membranes, with a marked preference for the insertion of triplets and multiples of triplets. The tendency of the mitochondrial channels to occur as extended arrays, apparently built up from triplets, may have important functional and evolutionary implications.