TIM/TOM complex

TheTIM/TOM complexis a protein complex in cellularbiochemistrywhich translocatesproteinsproduced from nuclearDNAthrough the mitochondrial membrane for use inoxidative phosphorylation.Inenzymology,the complex is described as anmitochondrial protein-transporting ATPase(EC7.4.2.3), or more systematicallyATP phosphohydrolase (mitochondrial protein-importing),as the TIM part requiresATPhydrolysis to work.

Simplified representation of the Mitochondrial DNA Organization proteins (top image). A close up of a single ribosome in coordination with the TOM complex on the outer Mitochondrial membrane and the TIM complex on the inner Mitochondrial membrane (bottom image). The nascent transmembrane protein is being fed into the mitochondrial membrane where its target peptide (not shown) gets cleaved.

mitochondrial protein-transporting ATPase
Identifiers
EC no.	7.4.2.3
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDBstructures	RCSB PDBPDBePDBsum
Gene Ontology	AmiGO/QuickGO
Search PMC articles PubMed articles NCBI proteins

Only 13 proteins necessary for amitochondrionare actually coded inmitochondrial DNA.The vast majority of proteins destined for the mitochondria are encoded in thenucleusand synthesised in the cytoplasm. These are tagged by an N-terminal or/and a C-terminal signal sequence. Following transport through thecytosolfrom the nucleus, the signal sequence is recognized by a receptor protein in thetranslocase of the outer membrane(TOM) complex. The signal sequence and adjacent portions of thepolypeptidechain are inserted in the TOM complex, then begin interaction with atranslocase of the inner membrane(TIM) complex, which are hypothesized to be transiently linked at sites of close contact between the two membranes. The signal sequence is then translocated into the matrix in a process that requires an electrochemical hydrogen ion gradient across the inner membrane. MitochondrialHsp70binds to regions of the polypeptide chain and maintains it in an unfolded state as it moves into the matrix.

The ATPase domain is essential during the interactions of the proteins Hsp70 and subunit Tim44.Without the presence of ATPase, carboxy-terminal segment is not able to bind to protein of Tim44.As mtHsp70 transmits the nucleotide state of the ATPase domain with alpha-helices A and B, Tim44 interacts with the peptide binding domain to coordinate the protein bind.

TIC/TOC Complex vs. TIM/TOM Complex

This protein complex is functionally analogous to theTIC/TOC complexlocated on the inner and outer membranes of the chloroplast, in the sense that it transports proteins into the membrane of the mitochondria. Although they both hydrolyze triphosphates, they are evolutionally unrelated.

References

• Bömer U, Meijer M, Maarse AC, Hönlinger A, Dekker PJ, Pfanner N, Rassow J (May 1997)."Multiple interactions of components mediating preprotein translocation across the inner mitochondrial membrane".The EMBO Journal.16(9): 2205–16.doi:10.1093/emboj/16.9.2205.PMC1169823.PMID9171336.
• Berthold J, Bauer MF, Schneider HC, Klaus C, Dietmeier K, Neupert W, Brunner M (June 1995)."The MIM complex mediates preprotein translocation across the mitochondrial inner membrane and couples it to the mt-Hsp70/ATP driving system".Cell.81(7): 1085–93.doi:10.1016/S0092-8674(05)80013-3.PMID7600576.
• Voos W, Martin H, Krimmer T, Pfanner N (November 1999). "Mechanisms of protein translocation into mitochondria".Biochimica et Biophysica Acta (BBA) - Reviews on Biomembranes.1422(3): 235–54.doi:10.1016/s0304-4157(99)00007-6.PMID10548718.

External links

• TCDB3.A.8- description of the entire complex
• Overview of the various import ways into mitochondria(group of N. Pfanner)
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