Tim9 and Tim10 make up the group of essential small Tim proteins that assist in transport of hydrophobic precursors across the intermembrane space in mammalian cells.
[1] Each subunit folds into a helix-loop-helix structure, with each loop forming a donut shape that comprises the upper face of the complex.
[1] Small Tim proteins are synthesised lacking a cleavable presequence, but instead containing internal targeting information and need to be imported to the intermembrane space.
[2] Mia40 is anchored to the mitochondrial inner membrane via an N-terminal hydrophobic segment, exposing a large domain to the intermembrane space.
Precursors are then released in oxidised state and form disulfide bridges which prevents their escape out of the intermembrane space.