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Cell Biology Lecture 223.18: Vesicular Transport
Clathrin
COP
Protein Trafficking -Vesicular
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Protein Trafficking -Vesicular
Protein Trafficking -Vesicular: Clathrin-coated pits
• Surface of clathrin coated vesicles and pits
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Protein Trafficking -Vesicular: Clathrin
• Clathrin structure: 3 heavy chains 3 light chains tripod structure
Protein Trafficking -Vesicular Budding
pit vesicle
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Protein Trafficking -Vesicular: SNAREs & Tethers
Energetically unfavourable process
Guidance of vesicles to the correct target membrane involves SNAREs and Tethers
Rab proteins facilitate capture
SNARE proteins facilitate docking and fusion
Rab on vesicles recognize tethering protein on membrane
Vesicle (v)-SNARES recognize Target (t)-SNARES
Protein Trafficking -Vesicular: Core Glycosylation
(enzymatic transfer of core oligosaccharide)
Protein modification begins in the ER:
Oligosaccharide linked to a phospholipid in er transferred to asparagine on polypeptide
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Protein Trafficking -Vesicular: ER to GOLGI
QUALITY CONTROL STARTS IN ER
• Chaperones
• Guide proteins in tertiary structure formation
• Hold back improperly folded conformations
• Safety mechanism
Correctly folded proteins that are to be retained in the ER have a C-terminal sequence of 4 aa called a ER retention signal. Typically the AA sequence is lys-asp-glu-leu (KDEL) (See Table 15-3)
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Proteins with ER retention signal (KDEL) transported to cis-GOLGI then returned to ER
Brefeldin A
Protein Trafficking -Vesicular: Golgi Apparatus
PROTEIN SORTING & MODIFICATION HUB: Cis face (entry) …receives vesicles from ER Trans face (exit) …dispatch vesicles to other organelles/ surface
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Protein Trafficking -Vesicular: Golgi Apparatus
GOLGI APPARATUS Near the nucleus Flattened membrane sacs: cisternae cis face (faces ER) and trans face (faces pm) Receives & releases transport vesicles
Protein Trafficking -Vesicular: Compartmentalization of GOLGI
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Protein Trafficking -Vesicular: ER to GOLGI
Protein Trafficking -ER to Surface - DEFAULT Constitutive secretion
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Lysosomes
Lysosomes
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Vacuoles
Vacuoles