Lecture 6: Vesicular Transport Parte 1

Definition of Vesicular Transport

when vesicles bud from a donor compartment and transport cargo to a target compartment

Cargo Definition (what is inside of a vesicle?)

soluble proteins, membrane proteins, & lipids.

Endo-memebrane System (what is it?) 

ER, Golgi, endoscopes, lysosomes, & transport vesicles, using vesicles to traffic cargo between them

Important Rule For Protein Transport 

What was in the cytosol in one organelle stays in the cytosol after vesicular transport 

COAT Proteins

proteins that DRIVE the budding process in vesicular transport

COPI Proteins 

COAT proteins for Golgi to ER transport 

COPII Proteins

COAT proteins for ER to Golgi transport

What starts the budding process/allows COAT proteins to come together

SAR1-GTP

SAR 1 (what is it)

• a monomeric GTP-ase that has it’s own GAPS & GEFS 

• a GTP-ase that changes it’s confirmation depending on it’s attachment (helix out or not) 

• recruits adaptor proteins that then start the budding process 

SAR1-GTP vs GDP 

when in the GTP bound form it recruits COPII adaptor proteins, when in the GDP bound form it does nothing. 

COP

COPII adaptor protein

proteins that

1. select cargo to be packaged 

2. intimate deformation of the ER membrane 

3. recruit outer coat proteins to help deform the bud 

Entire Budding Process

1. SAR1-GDP encounters a GEF and becomes SAR1-GTP, allowing it to bind to the ER membrane 

2. SAR1 attracts COPII adaptor proteins that select cargo, deform the membrane & recruit outer proteins 

How is cargo selected for transport

through EXIT SIGNALS on the protein (sol & mem & usually a AA seq)

The two possible fate of membrane proteins with exit signal s

1. reside in the membrane of another organelle

2. act as a cargo receptor for the soluble proteins & be recycled for use again

INNER Coat & OUTER Coat functions

• inner coat houses the cargo 

• outer coat deforms the membrane and recognizes the cargo receptor 

How vesicles get to their target?

A sequential targeting system that uses Rab & Tether Proteins, & SNARES

Rab Proteins

Proteins on the surface of the vesicle that are recognizes by tether proteins

SNARES

• V-Snare (on the vesicle) & T-Snares (on the target compartment)

• DOCK the vesicle 

How do vesicles fuse 

T & V Snares work together to pull the vesicle soooooooo close (1.5 nm) to then force the membranes to fuse