Translokacja białek do mitochondriów

Peptides carrying presequences targeted to the matrix are threaded through the TOM/TIM complex. Mitochondrial Hsp70 binds the peptide as it exits the TIM channel and moves it into the matrix, where the presequence is cleaved by matrix proteases.

Proteins targeted to the intermembrane space carry an additional hydrophobic signal sequence that stops translocation across the TIM complex. Signal peptidases cleave the hydrophobic segment and release the active protein in the intermembrane space.

Alternatively, mitochondrial intermembrane space assembly 40 or Mia40 protein imports intermembrane space proteins lacking the presequences.

Oxidized Mia40 forms a transient disulfide bond with the thiols on the incoming polypeptide and pulls the nascent peptide through the TOM channel. Once the entire peptide is threaded through, Mia40 is reduced.

Some inner membrane proteins with stop-transfer sequences are arrested and inserted into the membrane. Others are first processed by signal peptidases, and then recognized by an OXA  translocase, which embeds them in the membrane.