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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 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. The protein's name refers to this lattice structure, deriving from Latin clathri meaning lattice. Barbara Pearse named the protein clathrin at the suggestion of Graeme Mitchison, selecting it from three possible options. 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.
Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membrane can follow this pathway all the way to lysosomes for degradation or can be recycled back to the cell membrane in the endocytic cycle. Molecules are also transported to endosomes from the trans Golgi network and either continue to lysosomes or recycle back to the Golgi apparatus.
In cellular biology, pinocytosis, otherwise known as fluid endocytosis and bulk-phase pinocytosis, is a mode of endocytosis in which small molecules dissolved in extracellular fluid are brought into the cell through an invagination of the cell membrane, resulting in their containment within a small vesicle inside the cell. These pinocytotic vesicles then typically fuse with early endosomes to hydrolyze the particles.
Receptor-mediated endocytosis (RME), also called clathrin-mediated endocytosis, is a process by which cells absorb metabolites, hormones, proteins – and in some cases viruses – by the inward budding of the plasma membrane (invagination). This process forms vesicles containing the absorbed substances and is strictly mediated by receptors on the surface of the cell. Only the receptor-specific substances can enter the cell through this process.
The low-density lipoprotein receptor (LDL-R) is a mosaic protein of 839 amino acids that mediates the endocytosis of cholesterol-rich low-density lipoprotein (LDL). It is a cell-surface receptor that recognizes apolipoprotein B100 (ApoB100), which is embedded in the outer phospholipid layer of very low-density lipoprotein (VLDL), their remnants—i.e. intermediate-density lipoprotein (IDL), and LDL particles. The receptor also recognizes apolipoprotein E (ApoE) which is found in chylomicron remnants and IDL. In humans, the LDL receptor protein is encoded by the LDLR gene on chromosome 19. It belongs to the low density lipoprotein receptor gene family. It is most significantly expressed in bronchial epithelial cells and adrenal gland and cortex tissue.
Retromer is a complex of proteins that has been shown to be important in recycling transmembrane receptors from endosomes to the trans-Golgi network (TGN) and directly back to the plasma membrane. Mutations in retromer and its associated proteins have been linked to Alzheimer's and Parkinson's diseases.
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.
Low density lipoprotein receptor-related protein 2 also known as LRP-2 or megalin is a protein which in humans is encoded by the LRP2 gene.
Epidermal growth factor receptor substrate 15 is a protein that in humans is encoded by the EPS15 gene.
AP-2 complex subunit alpha-1 is a protein that in humans is encoded by the AP2A1 gene.
Clathrin heavy chain 1 is a protein that in humans is encoded by the CLTC gene.
Dynamin-1 is a protein that in humans is encoded by the DNM1 gene.
Sorting nexin-9 is a protein that in humans is encoded by the SNX9 gene.
Adaptor-associated protein kinase 1 also known as AP2-associated protein kinase 1 is an enzyme that in humans is encoded by the AAK1 gene and is involved in clathrin mediated endocytosis. Alternatively spliced transcript variants have been described, but their biological validity has not been determined.
The EHD protein family is a relatively small group of proteins which have been shown to play a role in several physiological functions, the most notable being the regulation of endocytotic vesicles. This family is recognized by its highly conserved EH domain, a structural motif that has been shown to facilitate specificity and interaction between protein and ligand. The four mammalian EHD proteins that have been classified are: EHD1, EHD2, EHD3, and EHD4.
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.
The C-terminal domain ofBeta2-adaptin is a protein domain is involved in cell trafficking by aiding import and export of substances in and out of the cell.
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
Ludger Johannes is a French-German biochemist who has specialized in the field of endocytosis and intracellular trafficking. He and his team study how sugars attached to proteins or lipids influence the transport of biological material into eukaryotic cells.
References
- ↑ Casamento A, Boucrot E (June 2020). "Molecular mechanism of Fast Endophilin-Mediated Endocytosis". The Biochemical Journal. 477 (12): 2327–2345. doi:10.1042/bcj20190342. PMC 7319585 . PMID 32589750.
- ↑ Rennick JJ, Johnston AP, Parton RG (March 2021). "Key principles and methods for studying the endocytosis of biological and nanoparticle therapeutics". Nature Nanotechnology. 16 (3): 266–276. Bibcode:2021NatNa..16..266R. doi: 10.1038/s41565-021-00858-8 . PMID 33712737. S2CID 232215301.
- 1 2 3 4 5 6 7 8 Boucrot, Emmanuel; Ferreira, Antonio P. A.; Almeida-Souza, Leonardo; Debard, Sylvain; Vallis, Yvonne; Howard, Gillian; Bertot, Laetitia; Sauvonnet, Nathalie; McMahon, Harvey T. (January 2015). "Endophilin marks and controls a clathrin-independent endocytic pathway". Nature. 517 (7535): 460–465. Bibcode:2015Natur.517..460B. doi:10.1038/nature14067. ISSN 0028-0836. PMID 25517094. S2CID 4470056. Archived from the original on 2022-10-12. Retrieved 2022-10-11.
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