Essential component of the TIM22 complex, a complex that mediates the import and insertion of multi-pass transmembrane proteins into the mitochondrial inner membrane. The TIM22 complex forms a twin-pore translocase that uses the membrane potential as external driving force. In the TIM22 complex, it acts as a docking point for the soluble TIM9-TIM10 heterohexamer that guides the target proteins in transit through the aqueous mitochondrial intermembrane space. Component of the TIM22 complex, whose core is composed of TIM18, TIM22 and TIM54, associated with the peripheral proteins MRS5/TIM12 and the 70 kDa heterohexamer composed of TIM9 and TIM10 (or TIM8 and TIM13). Interacts directly with both the TIM22 protein and the TIM9-TIM10 heterohexamer. Interacts with multi-pass transmembrane proteins in transit. The twin CX3C motif contains 4 conserved Cys residues that form 2 disulfide bonds in the mitochondrial intermembrane space. However, during the transit of TIM12 from cytoplasm into mitochondrion, the Cys residues probably coordinate zinc, thereby preventing folding and allowing its transfer across mitochondrial outer membrane (By similarity). Belongs to the small Tim family.