The mitochondrial import machinery for preproteins

Most mitochondrial proteins are transported from the cytosol into the organ elle. Due to the division of mitochondria into an outer and inner membrane, an intermembrane space and a matrix, an elaborated system for recognition and transport of preproteins has evolved. The translocase of the outer mito chondrial membrane (TOM) and the translocases of the inner mitochondrial me mbrane (TIM) mediate these processes. Receptor proteins on the cytosolic fa ce of mitochondria recognize the cargo proteins and transfer them to the ge neral import pore (GIP) of the outer membrane. Following the passage of pre proteins through the outer membrane they are transported with the aid of th e TIM23 complex into either the matrix, inner membrane, or intermembrane sp ace. Some preprotein families utilize the TIM22 complex for their insertion into the inner membrane. The identification of protein components, which a re involved in these transport processes, as well as significant insights i nto the molecular function of some of them, has been achieved in recent yea rs. Moreover, we are now approaching a new era in which elaborated techniqu es have already allowed and will enable us to gather information about the TOM and TIM complexes on an ultrastructural level.