InterPro domain: IPR038552

Tim21 is an essential component of the TIM23 complex, which mediates the translocation of transit peptide-containing proteins across the mitochondrial inner membrane. Tim21 is required to keep the TOM and the TIM23 complexes in close contact. At some point, it is released from the TOM23 complex to allow protein translocation into the mitochondrial matrix [ 1 , 2 ].

Tim21 consists of a single transmembrane segment in the inner membrane, and a large intermembrane space (IMS) domain that has been shown to bind to the IMS domain of the outer membrane of the Tom22 receptor [ 3 , 3 ]. The binding domain of Tim21 consists of a novel mixed alpha/beta fold [ 3 ].

1. Mitochondrial presequence translocase: switching between TOM tethering and motor recruitment involves Tim21 and Tim17. Cell 120, 817-29
2. Role of Tim21 in mitochondrial translocation contact sites. J. Biol. Chem. 280, 23437-40
3. The Tim21 binding domain connects the preprotein translocases of both mitochondrial membranes. EMBO Rep. 7, 1233-8