TIM / TOM complex

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Schematic representation of the TOM and TIM complexes in the mitochondrial membrane.

TIM / TOM complexes are multiprotein complexes in the mitochondrial double membrane and count among the translocases . They are responsible for ensuring that proteins that are synthesized in the cytosol, i.e. encoded by the nuclear DNA , can reach the mitochondria. In the end, only 13 proteins are encoded by mitochondrial DNA , the rest come from nuclear DNA. The TOM complex ( English Translocase of the Outer Membrane ) is built into the outer mitochondrial membrane, the TIM complex ( English Translocase of the Inner Membrane ) into the inner one. The proteins to be transported have either a presequence or an internal signal as a recognition sequence.

TOM complex

All proteins that are to be transported into the mitochondrion pass through the TOM complex, i.e. both matrix and intermembrane space and membrane proteins. The GIP (General Import Pore) is the central domain that transports the unfolded proteins across the membrane. Furthermore, TOM70 play an important role in the import of proteins with internal signals, TOM20 for proteins with a presequence, TOM40 and TOM22 as receptors during transport. Once the TOM complex has been overcome, the path splits up for each type of protein.

TIM complex

In the case of the TIM complexes, a basic distinction is made between the TIM22 and the TIM23 complex. The membrane potential is used as the driving force for transport .

The TIM23 complex or presequence translocase transports proteins with a presequence, which is split off in the matrix, into the matrix. The complex consists of TIM23, TIM17, TIM50 and TIM44 as import engines. After importing the protein, it is immediately bound by the mitochondrial heat shock protein mtHsp70.

The TIM22 complex transports proteins with an internal signal, which are built into the inner membrane. The complex is formed by TIM18, TIM22, TIM54 and TIM12; TIM9 and TIM10 help with the transport to the complex.

Intermembrane proteins and membrane proteins in the outer membrane do not use the TIM complex.

TIC / TOC complex

TIC / TOC complexes are multiprotein complexes in the double membrane of chloroplasts . The system works in a similar way.

Individual evidence

  1. ↑ a b c Peter Rehling and Chris Meisinger : Protein transport in mitochondria: TOM and TIM complexes. (PDF; 200 kB) BioSpectrum, accessed on March 20, 2020 .
  2. ^ Walter Neupert, Michael Brunner: The protein import motor of mitochondria . In: Nature Reviews Molecular Cell Biology . tape 3 , no. 8 , August 2002, ISSN  1471-0080 , p. 555-565 , doi : 10.1038 / nrm878 ( nature.com [accessed March 23, 2020]).
  3. ↑ Hayashi Yamamoto, Masatoshi Esaki, Takashi Kanamori, Yasushi Tamura, Shuh-ichi Nishikawa: Tim50 Is a Subunit of the TIM23 Complex that Links Protein Translocation across the Outer and Inner Mitochondrial Membranes . In: Cell . tape 111 , no. 4 , November 15, 2002, ISSN  0092-8674 , p. 519-528 , doi : 10.1016 / S0092-8674 (02) 01053-X , PMID 12437925 ( cell.com [accessed March 20, 2020]).