COPI: Diferenzas entre revisións
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Liña 34:
O ARF oscila cambia ciclicamente entre as conformacións unidas a [[GTP]] e [[GDP]]. Na forma unida a GTP, a conformación de ARF cambia de modo que o miristato e o N-terminal [[hidrófobo]] quedan máis expostos e asócianse coa membrana. A interconversión entre os estados unidos a GTP e GDP é mediado por ARF [[factor de intercambio do nucleótido guanina|factores de intercambio do nucleótido guanina]] ARF (GEFs) e [[proteína activadora da GTPase|proteínas activadoras da GTPase]] ARF (GAPs). Na membrana, o ARF-GTP é [[hidrólise|hidrolizado]] a ARF-GDP polas ARF GAPs. Unha vez na conformación unida ao GDP, o ARF pasa a unha conformación menos hidrófoba e disóciase da membrana. Os ARF-GDP solubles son convertidos de novo a ARF-GTP polas GEFs.
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:1. Luminal proteins: Proteins found in the lumen of the Golgi complex that need to be transported to the lumen of the ER contain the [[signal peptide]] [[KDEL (amino acid sequence)|KDEL]].<ref name="KDEL and KKXX retrieval">{{cite journal| author=Mariano Stornaiuolo| author2=Lavinia V. Lotti| author3=Nica Borgese| author4=Maria-Rosaria Torrisi| author5=Giovanna Mottola| author6=Gianluca Martire| author7=Stefano Bonatti| last-author-amp=yes|date=March 2003| title=KDEL and KKXX Retrieval Signals Appended to the Same Reporter Protein Determine Different Trafficking between Endoplasmic Reticulum, Intermediate Compartment, and Golgi Complex| journal=Molecular Biology of the Cell| volume=14|issue=3| pages=889–902| doi=10.1091/mbc.E02-08-0468| pmid=12631711| pmc=151567}}</ref> This sequence is recognized by a membrane-bound KDEL receptor. In yeast, this is [[Erd2p]] and in mammals it is [[KDELR]]. This receptor then binds to an ARF-GEF, a class of guanine nucleotide exchange factors. This protein in turn binds to the ARF. This interaction causes ARF to exchange its bound [[Guanosine diphosphate|GDP]] for [[Guanosine triphosphate|GTP]]. Once this exchange is made ARF binds to the cytosolic side of the cis-Golgi membrane and inserts the myristoylated N-terminal amphipathic alpha-helix into the membrane.<ref>{{Cite journal|last=Goldberg|first=J.|date=1998-10-16|title=Structural basis for activation of ARF GTPase: mechanisms of guanine nucleotide exchange and GTP-myristoyl switching|journal=Cell|volume=95|issue=2|pages=237–248|issn=0092-8674|pmid=9790530|doi=10.1016/s0092-8674(00)81754-7}}</ref>▼
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:2. Membrane proteins: Transmembrane proteins which reside in the ER contain sorting signals in their cytosolic tails which direct the protein to exit the Golgi and return to the ER. These sorting signals, or motifs, typically contain the amino acid sequence [[KKXX (amino acid sequence)|KKXX]] or KXKXX, which interact with COPI subunits α-COP and β'-COP.<ref name="KDEL and KKXX retrieval"/><ref name="Ma 926–937"/> The order in which adaptor proteins associate with cargo, or adaptor proteins associate with ARFs is unclear, however, in order to form a mature transport carrier coat protein, adaptor, cargo, and ARF must all associate.
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