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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