Protein targeting or protein sorting is the biological mechanism by which proteins are transported to their appropriate destinations within or outside the cell. Proteins can be targeted to the inner space of an organelle, different intracellular membranes, the plasma membrane, or to the exterior of the cell via secretion. Information contained in the protein itself directs this delivery process. Correct sorting is crucial for the cell; errors or dysfunction in sorting have been linked to multiple diseases.
Mitochondrial membrane transport proteins, also known as mitochondrial carrier proteins, are proteins which exist in the membranes of mitochondria. They serve to transport molecules and other factors, such as ions, into or out of the organelles. Mitochondria contain both an inner and outer membrane, separated by the inter-membrane space, or inner boundary membrane. The outer membrane is porous, whereas the inner membrane restricts the movement of all molecules. The two membranes also vary in membrane potential and pH. These factors play a role in the function of mitochondrial membrane transport proteins. There are 53 discovered human mitochondrial membrane transporters, with many others that are known to still need discovered.
Mitochondrial import inner membrane translocase subunit Tim8 A, also known as deafness-dystonia peptide or protein is an enzyme that in humans is encoded by the TIMM8A gene. This translocase has similarity to yeast mitochondrial proteins that are involved in the import of metabolite transporters from the cytoplasm into the mitochondrial inner membrane. The gene is mutated in deafness-dystonia syndrome and it is postulated that MTS/DFN-1 is a mitochondrial disease caused by a defective mitochondrial protein import system.
Mitochondrial import receptor subunit TOM22 homolog is a protein that in humans is encoded by the TOMM22 gene.
Mitochondrial import inner membrane translocase subunit Tim13 is an enzyme that in humans is encoded by the TIMM13 gene.
Mitochondrial import receptor subunit TOM34 is a protein that in humans is encoded by the TOMM34 gene.
The translocase of the outer membrane (TOM) is a complex of proteins found in the outer mitochondrial membrane of the mitochondria. It allows movement of proteins through this barrier and into the intermembrane space of the mitochondrion. Most of the proteins needed for mitochondrial function are encoded by the nucleus of the cell. The outer membrane of the mitochondrion is impermeable to large molecules greater than 5000 Daltons. The TOM works in conjunction with the translocase of the inner membrane (TIM) to translocate proteins into the mitochondrion. Many of the proteins in the TOM complex, such as TOMM22, were first identified in Neurospora crassa and Saccharomyces cerevisiae. Many of the genes encoding these proteins are designated as TOMM (translocase of the outer mitochondrial membrane) complex genes.
Metaxin 1, also known as MTX1, is a protein which in humans is encoded by the MTX1 gene.
Mitochondrial import inner membrane translocase subunit TIM44 is an enzyme that in humans is encoded by the TIMM44 gene.
Mitochondrial import inner membrane translocase subunit Tim9 B is an enzyme that in humans is encoded by the FXC1 gene.
Mitochondrial import receptor subunit TOM70 is a protein that in humans is encoded by the TOMM70A gene.
Mitochondrial import inner membrane translocase subunit Tim23 is an enzyme that in humans is encoded by the TIMM23 gene.
Mitochondrial import inner membrane translocase subunit Tim17-A is an enzyme that in humans is encoded by the TIMM17A gene.
Translocase of outer mitochondrial membrane 40 homolog (yeast), also known as TOMM40, is a protein which in humans is encoded by the TOMM40 gene.
Mitochondrial import inner membrane translocase subunit Tim9 is an enzyme that in humans is encoded by the TIMM9 gene.
Mitochondrial import inner membrane translocase subunit Tim22 is an enzyme that in humans is encoded by the TIMM22 gene.
Mitochondrial import inner membrane translocase subunit TIM50 is a protein that in humans is encoded by the TIMM50 gene. Tim50 is a subunit of the Tim23 translocase complex in the inner mitochondrial membrane. Mutations in TIMM50 can lead to epilepsy, severe intellectual disability, and 3-methylglutaconic aciduria. TIMM50 expression is increased in breast cancer cells and decreased in hypertrophic hearts.
The translocase of the inner membrane (TIM) is a complex of proteins found in the inner mitochondrial membrane of the mitochondria. Components of the TIM complex facilitate the translocation of proteins across the inner membrane and into the mitochondrial matrix. They also facilitate the insertion of proteins into the inner mitochondrial membrane, where they must reside in order to function, these mainly include members of the mitochondrial carrier family of proteins.
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. Both Tim9 and Tim10 form a hexamer, the Tim9-Tim10 complex, that when associated, functions as a chaperone to assist translocation of preproteins from the outer mitochondrial membrane to the translocase of the inner membrane. The functional Tim9-Tim10 complex not only directs preproteins to the inner mitochondrial membrane in order to interact with the TIM22 complex, but also guides β-barrel precursor proteins to the sorting and assembly machinery (SAM) of the outer membrane.
ADP/ATP translocase 3, also known as solute carrier family 25 member 6, is a protein that in humans is encoded by the SLC25A6 gene.
