β-barrel proteins are present in the outer membrane of Gram-negative bacteria and of organel- les of endosymbiotic origin, i.e. mitochondria and chloroplasts where they perform a variety of functions. Mitochondrial β-barrel proteins are important for protein import, metabolite transport and the organelle morphology and distribution. They also seem to play a crucial role in mitochondria evolution. Quite recently a specific pathway for the insertion of β-barrel proteins was identified in both mitochondria and Gram-negative bacteria and was proved to be conserved during evolution.

The primary role in the course of protein import into mitochondria play channels allow translocation of proteins through the mitochondrial membrane and their incorporation into the area of the membranes. In the outer mitochondrial membrane import channel is located TOM complex (translocase of the outer membrane of the) channel and participating in the folding of proteins with complex structure keg b TOB (the topogenesis of mitochondrial outer membrane?-Barrel proteins). In turn, in the intima of the two channels are located on a separate substrate specificity.

The majority of mitochondrial proteins imported from the cytosol. The main role in this process is played by protein complexes located in the outer and inner mitochondrial membrane. These outer membrane translocase complex TOM), and intimal translocation complexes (TIM). The components of an imported proteins recognize and enable their translocation across membranes or their incorporation into the film. The dynamic nature of both types of translocase allows the sorting of proteins with different mechanisms of imports.