Sandbox8999: Difference between revisions
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There are various endocytic mechanisms by which eukaryotic cells bring proteins and lipids into the cell, however clathrin-mediated endocytosis is known to be the most informative pathway to date. Other portals for endocytic entry include phagocytosis and macropinocytosis.<ref name="mcpherson"> McPherson, P. S., Ritter, B., & Wendland, B. Clathrin-Mediated Endocytosis. (2009). Clathrin-Mediated Endocytosis. In Trafficking Inside Cells: Pathways, Mechanisms, and Regulation (Section II). [http://dx.doi.org/10.1007/978-0-387-93877-6_9 doi: 10.1007/978-0-387-93877-6_9]</ref> Endocytic events are initiated through the activity of the clathrin coat and adaptor proteins that select the “cargo” that will be carried into the cell in vesicles.<ref name ="johnson"> Johnson, G. T., & Goodsell, D. (2007). Molecule of the Month: Clathrin. [http://dx.doi.org/10.2210/rcsb_pdb/mom_2007_4 doi: 10.2210/rcsb_pdb/mom_2007_4]</ref> At least 20 clathrin adaptors have been identified, and they all recognize and bind to membrane proteins or phospholipids that are specific for a certain organelle.<ref name ="johnson"> Johnson, G. T., & Goodsell, D. (2007). Molecule of the Month: Clathrin. [http://dx.doi.org/10.2210/rcsb_pdb/mom_2007_4 doi: 10.2210/rcsb_pdb/mom_2007_4]</ref> The formation of most cellular vesicles are facilitated by these coat-proteins like clathrin.<ref name ="johnson"> Johnson, G. T., & Goodsell, D. (2007). Molecule of the Month: Clathrin. [http://dx.doi.org/10.2210/rcsb_pdb/mom_2007_4 doi: 10.2210/rcsb_pdb/mom_2007_4]</ref> Cells endocytose vesicles from the plasma membrane to perform housekeeping tasks such as taking up nutrients, importing signaling receptors, mediating immune responses, cleaning up cell debris, or providing a pathway for pathogens or toxins.<ref name ="johnson"> Johnson, G. T., & Goodsell, D. (2007). Molecule of the Month: Clathrin. [http://dx.doi.org/10.2210/rcsb_pdb/mom_2007_4 doi: 10.2210/rcsb_pdb/mom_2007_4]</ref> | There are various endocytic mechanisms by which eukaryotic cells bring proteins and lipids into the cell, however clathrin-mediated endocytosis is known to be the most informative pathway to date. Other portals for endocytic entry include phagocytosis and macropinocytosis.<ref name="mcpherson"> McPherson, P. S., Ritter, B., & Wendland, B. Clathrin-Mediated Endocytosis. (2009). Clathrin-Mediated Endocytosis. In Trafficking Inside Cells: Pathways, Mechanisms, and Regulation (Section II). [http://dx.doi.org/10.1007/978-0-387-93877-6_9 doi: 10.1007/978-0-387-93877-6_9]</ref> Endocytic events are initiated through the activity of the clathrin coat and adaptor proteins that select the “cargo” that will be carried into the cell in vesicles.<ref name ="johnson"> Johnson, G. T., & Goodsell, D. (2007). Molecule of the Month: Clathrin. [http://dx.doi.org/10.2210/rcsb_pdb/mom_2007_4 doi: 10.2210/rcsb_pdb/mom_2007_4]</ref> At least 20 clathrin adaptors have been identified, and they all recognize and bind to membrane proteins or phospholipids that are specific for a certain organelle.<ref name ="johnson"> Johnson, G. T., & Goodsell, D. (2007). Molecule of the Month: Clathrin. [http://dx.doi.org/10.2210/rcsb_pdb/mom_2007_4 doi: 10.2210/rcsb_pdb/mom_2007_4]</ref> The formation of most cellular vesicles are facilitated by these coat-proteins like clathrin.<ref name ="johnson"> Johnson, G. T., & Goodsell, D. (2007). Molecule of the Month: Clathrin. [http://dx.doi.org/10.2210/rcsb_pdb/mom_2007_4 doi: 10.2210/rcsb_pdb/mom_2007_4]</ref> Cells endocytose vesicles from the plasma membrane to perform housekeeping tasks such as taking up nutrients, importing signaling receptors, mediating immune responses, cleaning up cell debris, or providing a pathway for pathogens or toxins.<ref name ="johnson"> Johnson, G. T., & Goodsell, D. (2007). Molecule of the Month: Clathrin. [http://dx.doi.org/10.2210/rcsb_pdb/mom_2007_4 doi: 10.2210/rcsb_pdb/mom_2007_4]</ref> | ||
The canonical clathrin pathway is referred to as the clathrin coated pits and the coated vesicles of endocytosis, whereas the noncanonical clathrin pathway is related to the clathrin-actin assembles of phagocytotic processes.<ref name="harrison" /> | |||
'''The Canonical | '''The Canonical Pathway''' | ||
Classical endocytosis involving clathrin-coated pits and clathrin-coated vesicles is referred to as the '''canonical clathrin pathway'''.<ref name="harrison" /> Canonical clathrin-dependent pathways involve the uptake of transferrin (Tf) by transferrin receptor (TfR) and the uptake of LDL by LDL receptors (LDLR).<ref name="harrison" /> Early studies showed that LDL epidermal growth factor (Tf) bound to their specific receptors could be endocytosed within the same vesicle.<ref name="harrison" /> The receptors for these molecules are composed of tails on their cytoplasmic side that contain sequences, which determine cargo sorting and also signal for clathrin to bind.<ref name="harrison" /> Clathrin then coats these vesicles and endocytosis occurs.<ref name="harrison" /> Other pathways, such as reuptake of neurotransmitters into the synaptic cleft, are seen to have similar mechanisms to canonical clathrin pathways.<ref name="harrison" /> | |||
'''The Noncanonical Pathway''' | |||
The '''noncanonical clathrin pathway''' refers to clathrin-actin assemblies, which form phagocytotic vesicles in response to invading bacterium.<ref name="harrison" /> Pathogen invasion into nonphagocytic cells result in the recruitment of clathrin.<ref name="harrison" /> These pathogens invade the cell through a process called the “zippering” mechanism, in which actin filaments are utilized to surround the pathogens with the host-cell membrane.<ref name="harrison" /> Actin recruitment requires the formation of clathrin patches and thus the clathrin-assembly forms.<ref name="harrison" /> Actin is not usually needed in classical endocytosis, but it is required when the size of the cargo in the forming vesicle is too large for the vesicle to close.<ref name="harrison" /> This association between actin and clathrin is unique to this pathway and distinguishes the noncanonical from the canonical pathway.<ref name="harrison" /> | The '''noncanonical clathrin pathway''' refers to clathrin-actin assemblies, which form phagocytotic vesicles in response to invading bacterium.<ref name="harrison" /> Pathogen invasion into nonphagocytic cells result in the recruitment of clathrin.<ref name="harrison" /> These pathogens invade the cell through a process called the “zippering” mechanism, in which actin filaments are utilized to surround the pathogens with the host-cell membrane.<ref name="harrison" /> Actin recruitment requires the formation of clathrin patches and thus the clathrin-assembly forms.<ref name="harrison" /> Actin is not usually needed in classical endocytosis, but it is required when the size of the cargo in the forming vesicle is too large for the vesicle to close.<ref name="harrison" /> This association between actin and clathrin is unique to this pathway and distinguishes the noncanonical from the canonical pathway.<ref name="harrison" /> | ||
