Protein translocation into mitochondria: the role of TIM complexes

Import of nuclear-encoded mitochondrial preproteins is mediated by a genera l translocase in the outer membrane, the TOM complex, and by two distinct t ranslocases in the mitochondrial inner membrane, the TIM23 complex and the TIM22 complex. Both TIM complexes cooperate with the TOM complex but facili tate import of different classes of precursor proteins. Precursors with an N-terminal presequence are imported via the TIM23 complex, whereas mitochon drial carrier proteins require the TIM22 complex for insertion into the inn er membrane. This review discusses recent advances in understanding the str ucture and function of the translocases of the inner membrane and the possi ble role of Tim proteins in the development of the Mohr-Tranebjaerg syndrom e, a mitochondrial disorder leading to neurodegeneration.