The key difference between TIM and TOM complex is that TIM (translocase of the inner membrane) complex is a complex of proteins found in the inner mitochondrial membrane of mitochondria while TOM (translocase of the outer membrane) complex is a complex of proteins found in the outer mitochondrial membrane of the mitochondria.
TIM and TOM complexes are two complexes of proteins in the mitochondrial inner and outer membranes that translocate proteins produced from nuclear DNA through the mitochondrial membrane for use in oxidative phosphorylation. They are very important in cellular biochemistry. Moreover, these protein complexes are functionary analogous to the TIC and TOC protein complexes located in the inner and outer membranes of the chloroplast.
CONTENTS
1. Overview and Key Difference
2. What is TIM Complex
3. What is TOM Complex
4. Similarities – TIM and TOM Complex
5. TIM vs TOM Complex in Tabular Form
6. Summary – TIM vs TOM Complex
What is TIM Complex?
TIM complex is a complex of proteins found in the inner mitochondrial membrane of the mitochondria. The components of the TIM complex facilitate the translocation of proteins across the inner membrane and to the mitochondrial matrix. They also normally must reside in the inner mitochondrial membrane in order to facilitate the insertion of proteins into the inner mitochondrial membrane. This complex mainly includes members of the mitochondrial carrier family of proteins. Several TIM complexes have been identified, such as TIM22 and TIM23.
Moreover, TIM22 is responsible for mediating the integration of carrier preprotein into the inner membrane. Tim22 is a subunit of the TIM22 complex, which forms a channel within the inner membrane. It is referred to as carrier translocase. Tim54 and small Tim proteins such as Tim9, Tim10, and Tim12 also contributed to the TIM22 complex. Tim 18 is also in this complex; however, its function is not yet known. Furthermore, the TIM23 complex facilitates the translocation of matrix targeted proteins into the mitochondrial matrix. These proteins contain cleavable presequence. This complex is made up of subunits such as Tim 17, Tim21, and Tim23, which contribute to the structural formation of the translocation channel that spans the inner membrane, while Tim 44 is a peripheral membrane protein.
What is TOM Complex?
TOM complex is a complex of proteins that is found in the outer mitochondrial membrane of the mitochondria. It allows the movement of proteins through this barrier and into the intermembrane space of the mitochondria. Most of the proteins that are needed for mitochondrial function are encoded by the nucleus of the cell. The outer membrane of the mitochondria is impermeable to large molecules. The TOM and TIM complexes together translocate large proteins inside the mitochondria. Moreover, many of the proteins in the TOM complex, such as TOMM22 were first identified in organisms like Neurospora crassa and Saccharomyces cerevisiae.
Furthermore, the TOM complex forms a complex made of Tom 70, Tom 22, Tom 20, Tom 40, Tom 7, Tom 6 and Tom 5. Tom 22 and Tom 20 are preprotein receptors that are responsible for the recognition of the cleavable presequence possessed by mitochondrial-targeted proteins. Tom 70 is also a preprotein that is mainly responsible for the recognition of non-cleavable preproteins and acts as a point for chaperone binding. Tom40 is a core element of the translocase complex and complexes with Tom22. Tom40 forms the central protein conducting channel with a diameter of approximately 2.5nm.
What are the Similarities Between TIM and TOM Complex?
- TIM and TOM complex are two complexes of proteins in the mitochondrial inner and outer membranes.
- Both complexes facilitate translocating proteins produced from nuclear DNA through the mitochondrial membrane for use in oxidative phosphorylation.
- Both complexes are functionary analogous to TIC and TOC protein complexes located on the inner and outer membranes of the chloroplast.
- These complexes facilitate the translocation of impermeable large protein molecules greater than 500 Daltons.
- They work in conjunction with each other in order to translocate proteins into the mitochondrial matrix.
What is the Difference Between TIM and TOM Complex?
TIM complex is found in the inner mitochondrial membrane of the mitochondria, while TOM complex is found in the outer mitochondrial membrane of the mitochondria. Thus, this is the key difference between TIM and TOM complex. Furthermore, TIM complex has a molecular weight of 440 kDa, while TOM complex has a molecular weight of 400 to 600 kDa.
The below infographic presents the differences between TIM and TOM complex in tabular form for side by side comparison.
Summary – TIM vs TOM Complex
TIM and TOM complex are two complexes of proteins that are very useful in cellular biochemistry. They facilitate the translocation of proteins that are produced from nuclear DNA through the mitochondrial membrane for use in oxidative phosphorylation. TIM complex is found in the inner mitochondrial membrane of the mitochondria, while TOM complex is found in the outer mitochondrial membrane of the mitochondria. So, this summarizes the difference between TIM and TOM complex.
Reference:
1. “Tim/Tom Complex.” An Overview | ScienceDirect Topics.
2. Pitt, Ashley S, and Susan K Buchanan. “A Biochemical and Structural Understanding of Tom Complex Interactions and Implications for Human Health and Disease.” Cells, MDPI.
Image Courtesy:
1. “Mitochondrial protein import” By Rtian96 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Mitochondrial dna organization cartoon” By Francisco J Iborra1 , Hiroshi Kimura2 and Peter R Cook – The functional organization of mitochondrial genomes in human cells (CC BY 2.0) via Commons Wikimedia