A presequence- and voltage-sensitive channel of the mitochondrial preprotein translocase formed by Tim23

Proteins imported into the mitochondrial matrix are synthesized in the cyto sol with an N-terminal presequence and are translocated through hetero-olig omeric translocase complexes of the outer and inner mitochondrial membranes . The channel across the inner membrane is formed by the presequence transl ocase, which consists of roughly six distinct subunits; however, it is not known which subunits actually form the channel. Here we report that purifie d Tim23 forms a hydrophilic, similar to 13-24 Angstrom wide channel charact eristic of the mitochondrial presequence translocase. The Tim23 channel is cation selective and activated by a membrane potential and presequences. Th e channel is formed by the C-terminal domain of Tim23 alone, whereas the N- terminal domain is required for selectivity and a high-affinity presequence interaction. Thus, Tim23 forms a voltage-sensitive high-conductance channe l with specificity for mitochondrial presequences.