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Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. Endocytosis includes pinocytosis and phagocytosis. It is a form of active transport.
Clathrin is a protein that plays a major role in the formation of coated vesicles. Clathrin was first isolated and named by Barbara Pearse in 1976. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. When the triskelia interact they form a polyhedral lattice that surrounds the vesicle, hence the protein's name, which is derived from the Latin clathrum meaning lattice. Coat-proteins, like clathrin, are used to build small vesicles in order to transport molecules within cells. The endocytosis and exocytosis of vesicles allows cells to communicate, to transfer nutrients, to import signaling receptors, to mediate an immune response after sampling the extracellular world, and to clean up the cell debris left by tissue inflammation. The endocytic pathway can be hijacked by viruses and other pathogens in order to gain entry to the cell during infection.
COPI is a coatomer, a protein complex that coats vesicles transporting proteins from the cis end of the Golgi complex back to the rough endoplasmic reticulum (ER), where they were originally synthesized, and between Golgi compartments. This type of transport is retrograde transport, in contrast to the anterograde transport associated with the COPII protein. The name "COPI" refers to the specific coat protein complex that initiates the budding process on the cis-Golgi membrane. The coat consists of large protein subcomplexes that are made of seven different protein subunits, namely α, β, β', γ, δ, ε and ζ.
Mark Steven Bretscher is a British biological scientist and Fellow of the Royal Society. He worked at the Medical Research Council Laboratory of Molecular Biology in Cambridge, United Kingdom and is currently retired.
Vesicular transport adaptor proteins are proteins involved in forming complexes that function in the trafficking of molecules from one subcellular location to another. These complexes concentrate the correct cargo molecules in vesicles that bud or extrude off of one organelle and travel to another location, where the cargo is delivered. While some of the details of how these adaptor proteins achieve their trafficking specificity has been worked out, there is still much to be learned.
AP180 is a protein that plays an important role in clathrin-mediated endocytosis of synaptic vesicles. It is capable of simultaneously binding both membrane lipids and clathrin and is therefore thought to recruit clathrin to the membrane of newly invaginating vesicles. In Drosophila melanogaster, deletion of the AP180 homologue, leads to enlarged but much fewer vesicles and an overall decrease in transmitter release. In D. melanogaster it was also shown that AP180 is also required for either recycling vesicle proteins and/or maintaining the distribution of both vesicle and synaptic proteins in the nerve terminal. A ubiquitous form of the protein in mammals, CALM, is named after its association with myeloid and lymphoid leukemias where some translocations map to this gene. The C-terminus of AP180 is a powerful and specific inhibitor of clathrin-mediated endocytosis.
The ANTH domain is a membrane binding domain that shows weak specificity for PtdIns(4,5)P2. It was found in AP180 endocytotic accessory protein that has been implicated in the formation of clathrin-coated pits. The domain is involved in phosphatidylinositol 4,5-bisphosphate binding and is a universal adaptor for nucleation of clathrin coats.
The AP2 adaptor complex is a multimeric protein that works on the cell membrane to internalize cargo in clathrin-mediated endocytosis. It is a stable complex of four adaptins which give rise to a structure that has a core domain and two appendage domains attached to the core domain by polypeptide linkers. These appendage domains are sometimes called 'ears'. The core domain binds to the membrane and to cargo destined for internalisation. The alpha and beta appendage domains bind to accessory proteins and to clathrin. Their interactions allow the temporal and spatial regulation of the assembly of clathrin-coated vesicles and their endocytosis.
AP-2 complex subunit mu is a protein that in humans is encoded by the AP2M1 gene.
AP-1 complex subunit mu-1 is a protein that in humans is encoded by the AP1M1 gene.
AP-1 complex subunit gamma-1 is a protein that in humans is encoded by the AP1G1 gene.
AP-1 complex subunit beta-1 is a protein that in humans is encoded by the AP1B1 gene.
AP-2 complex subunit beta is a protein that in humans is encoded by the AP2B1 gene.
AP-1 complex subunit sigma-1A is a protein that in humans is encoded by the AP1S1 gene.
AP-1 complex subunit sigma-2 is a protein that in humans is encoded by the AP1S2 gene.
Clathrin adaptor proteins, also known as adaptins, are vesicular transport adaptor proteins associated with clathrin. These proteins are synthesized in the ribosomes, processed in the endoplasmic reticulum and transported from the Golgi apparatus to the trans-Golgi network, and from there via small carrier vesicles to their final destination compartment. The association between adaptins and clathrin are important for vesicular cargo selection and transporting. Clathrin coats contain both clathrin and adaptor complexes that link clathrin to receptors in coated vesicles. Clathrin-associated protein complexes are believed to interact with the cytoplasmic tails of membrane proteins, leading to their selection and concentration. Therefore, adaptor proteins are responsible for the recruitment of cargo molecules into a growing clathrin-coated pits. The two major types of clathrin adaptor complexes are the heterotetrameric vesicular transport adaptor proteins (AP1-5), and the monomeric GGA adaptors. Adaptins are distantly related to the other main type of vesicular transport proteins, the coatomer subunits, sharing between 16% and 26% of their amino acid sequence.
Margaret Scott Robinson FRS FMedSci is a British molecular cell biologist, a professor and researcher in the Cambridge Institute for Medical Research, at the University of Cambridge.
Exomer is a heterotetrameric protein complex similar to COPI and other adaptins. It was first described in the yeast Saccharomyces cerevisiae. Exomer is a cargo adaptor important in transporting molecules from the Golgi apparatus toward the cell membrane. The vesicles it is found on are different from COPI vesicles in that they do not appear to have a "coat" or "scaffold" around them.
The muniscin protein family was initially defined in 2009 as proteins having 2 homologous domains that are involved in clathrin mediated endocytosis (CME) and have been reviewed. In addition to FCHO1, FCHO2 and Syp1, SGIP1 is also included in the family because it contains the μ (mu) homology domain and is involved in CME, even though it does not contain the F-BAR domain
Frances Brodsky is an American cell biologist. She is known for her work on clathrin and its role in the function of the immune system. She is a professor of cell biology and the director of the Division of Biosciences at University College London. She is the author of three scientific mystery novels under the pseudonym B.B. Jordan. She was the founding editor of the journal Traffic.
References
- 1 2 3 "Pearse, Barbara Mary Frances, (Mrs M. S. Bretscher)" . Who's Who . Vol. 2014 (online Oxford University Press ed.). A & C Black.(Subscription or UK public library membership required.)
- ↑ Pearse, B. M. (1987). "Clathrin and coated vesicles". The EMBO Journal. 6 (9): 2507–12. doi:10.1002/j.1460-2075.1987.tb02536.x. PMC 553666 . PMID 2890519.
- ↑ Pearse, B. M. (1988). "Receptors compete for adaptors found in plasma membrane coated pits". The EMBO Journal. 7 (11): 3331–6. doi:10.1002/j.1460-2075.1988.tb03204.x. PMC 454828 . PMID 2905261.
- ↑ Pearse, B. M. F.; Robinson, M. S. (1990). "Clathrin, Adaptors, and Sorting". Annual Review of Cell Biology. 6: 151–171. doi:10.1146/annurev.cb.06.110190.001055. PMID 2177341.
- ↑ Ford, M. G.; Pearse, B. M.; Higgins, M. K.; Vallis, Y; Owen, D. J.; Gibson, A; Hopkins, C. R.; Evans, P. R.; McMahon, H. T. (2001). "Simultaneous binding of Ptd Ins(4,5)P2 and clathrin by AP180 in the nucleation of clathrin lattices on membranes". Science. 291 (5506): 1051–5. Bibcode:2001Sci...291.1051F. CiteSeerX 10.1.1.407.6006 . doi:10.1126/science.291.5506.1051. PMID 11161218.
- ↑ Pearse, B. M. F. (1975). "Coated vesicles from pig brain: Purification and biochemical characterization". Journal of Molecular Biology. 97 (1): 93–98. doi:10.1016/S0022-2836(75)80024-6. PMID 1177317.
- ↑ Pearse, B. M. F.; Bretscher, M. S. (1981). "Membrane Recycling by Coated Vesicles". Annual Review of Biochemistry. 50: 85–101. doi:10.1146/annurev.bi.50.070181.000505. PMID 7023370.
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