Essential Molecular Biology (BIOC0007) Notes - Protein Trafficking and Translocation
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Course
Essential Molecular Biology (BIOC0007)
Institution
University College London (UCL)
Explore Essential Molecular Biology at UCL. Navigate the intricate realm of protein trafficking and translocation, unraveling the dynamics of protein movement from the ER. These notes, tailored for Year 1 students, provide a humanized academic guide, enhancing your comprehension of essential molecu...
Protein Trafficking and Translocation – Summary
Protein Trafficking from the ER
ER – endoplasmic reticulum
o ER = starting place for proteins destined for other locations
Once protein translocated into or through ER membrane
glycosylated and folded
Pass ER quality control transported to Golgi complex
From Golgi transported to various different locations
Some proteins are maintained on the ER = ER resident
proteins
Trafficking routes from the ER
o Proteins can be resident to a compartment – or go to another
Biosynthetic / secretory pathway
Proteins from ER through golgi complex cell surface + endosomes + lysosomes
Endocytic pathway
Early endosome
o First compartment reaches by endocytosis of proteins from cell surface
Protein coming into cell by endocytosis taken up into endocytic
vesicles first to early endosome
Late endosome
o Protein travels further in endocytic pathway – reaching late endosome
Lysosome = final component of endocytic pathway
Retrograde / recycling pathways
To balance out forward protein transport pathway
Signals direct proteins to the correct compartment
o Signals can be:
Amino acid sequences
Signal sequences
Signal patches
o Protein modifications
Glycosylation – sugars added to protein
Ubiquitination – addition of ubiquitin protein to other proteins
Lipid modification – lipids added to protein
Protein transport between membrane bound compartments
o Vesicular transport
Vesicular transport = mechanism to transport from one
compartment to another without membranes
Donor compartment vesicle budding containing
protein vesicle movement via cytoskeletal
elements vesicle fusion with target compartment
o Direct fusion
One compartment fusion with the next compartment
forming hybrid organelle
Protein coats
o Many transport vesicles have electron dense coats
Have protein to select right proteins to go into vesicle + structural proteins which allow
vesicle to form
o Membrane deforms into budding vesicle using coat proteins
Selecting right proteins in vesicle
Some membrane proteins interact with coat proteins
, Protein Trafficking and Translocation – Summary
Other proteins need a receptor to enter vesicle = cargo-receptor
Some proteins without signals enter vesicle – as they are in cytosol
Membrane cargo-receptor protein
Bind to soluble cargo proteins concentrating them in vesicles
V-SNARE proteins
Required for vesicle fusion
GTP-binding proteins
Required for vesicle fusion + as part of the coat
o Coated vesicles involved in protein trafficking – different coats = different transport steps
COPII vesicle
Takes proteins from ER to cis-golgi (first compartment of golgi)
Coat proteins = Sec23/Sec24 + Sec13/Sec31 complexes + Sec16
Associated GTPase = Sar1
COPI vesicle
Takes proteins from cis-golgi to ER
Takes proteins from later to earlier golgi cisternae
Coat proteins = coatomers containing seven different COP subunits
Associated GTPase = ARF
Clathrin coated vesicles
Clathrin as structural protein + associated adapter proteins
o Clathrin + AP1 complexes / GGA – take proteins from trans-golgi to
endosome
Associated GTPase = ARF
o Clathrin + AP2 complexes– take proteins from plasma membrane to
endosome
Associated GTPase = ARF
o AP3 complexes – takes proteins from golgi to lysosome, melanosome, or
platelet vesicles
Associated GTPase = ARF
GTPases ARF and Sar1
Control coat recruitment
Also control disassembly of COPI and II coated vesicles
Uncoated of clathrin-coated vesicles requires an Hsp70 family ATPase
o Assembly and disassembly of a coated vesicle – clathrin coated vesicle
Coat assembly and cargo selection
Receptor proteins on cell surface which bind to soluble cargo molecules
Ails of receptors are recognised by adaptor complex
Bud formation
Adaptor complex recruits clathrin
Resulting in deformation of membrane forming a bud
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