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Ion channel proteins provide a pathway for movement of ions across the hostile, low-dielectric environment of the membrane. New work on crystalline bacterial K+ channels shows that this process is optimized for the natural substrate, K+. An additional high resolution structure of the channel illustrates how the protein provides prosthetic solvation for the ion — and also a beautiful picture of how water itself solvates the ion.
After reconstitution into liposomes, Tim23p, a mitochondrial inner membrane protein required for protein import, forms an aqueous pore that is activated by a transmembrane potential and mitochondrial targeting peptides. A report in this issue suggests that proteins are translocated into the mitochondrial matrix through a channel formed by Tim23p. These data also suggest a mechanism by which protein import can occur without disrupting the permeablility barrier of the inner membrane.