Lecture 11: Types of Vesicle Transport and Lysosomes

Question 1

COPI- coated vesicles

Answer 1

• Move cargo backwards
• From ERGIC/Golgi to ER
• From Trans to cis golgi

Question 2

COPII-coated vesicles

Answer 2

• Moves cargo forward (ER to Golgi complex)

Question 3

Clathrin-coated vesicles

Answer 3

• Move materials from the TGN to endosomes, lysosomes, plant vacuoles and endocytosis (Clathrin coated vesicles (CCVs) mediate endocytosis of plasma membrane proteins and deliver their content to the endosomes for either subsequent recycling to the plasma membrane or transport to the vacuole for degradation.)

Question 4

TGN

Answer 4

The CGN is the first cisternal structure, and the TGN is the final, from which proteins are packaged into vesicles destined to lysosomes, secretory vesicles, or the cell surface.

Question 5

Endosomes vs vesicles

Answer 5

• ## Endosomes are typically involved with the sorting and delivery of lipid vesicles and their contents to and from the plasma membrane. ‘Early’ endosomes are positioned close to sites of active endocytosis, where they can act as a recycling compartment for vesicles budding from the plasma membrane.

Question 6

Protein pathway for degradation

Answer 6

• Proteins destined to degradation are transported from early endosomes to late endosomes and lysosomes, where degradation takes place

Question 7

Early endosomes

Answer 7

Early endosomes receive membrane proteins and lipids delivered into the cell by clathrin-dependent endocytosis. The amount of protein and lipid entering the early endosomal compartment is enormous, given that bulk plasma membrane is internalized at rates as high as 2% per minute and nutrient receptors such as transferrin receptor (which binds iron-bound ferritin) are internalized at rates exceeding 20% per minute. Remarkably, the majority of this internalized material (approximately 90% of internalized protein and lipid and 60% to 70% of all internalized fluid) is rapidly recycled to the cell surface from early endosomes. The rest of the membrane and contents are routed to lysosomes for degradation. This sorting of proteins and lipids in endosomes depends on the following features.

Question 8

COPII select and concentrate certain proteins for transport in vesicles by:

Answer 8

interacting with transmembrane proteins that have ER export signals (on cytosolic side)

Question 9

COPII vesicles usually contain

Answer 9

• enzymes destined for the Golgi complex (ex: glycosyltransferases)
• Proteins involved in vesicle docking and fusion
• Proteins that bind soluble cargo (soluble protein suppose to be secreted by the cell)

Question 10

How COPII coated protein bend the membrane for budding? (6)

Answer 10

• Sar1-GDP is recruited by GEF (guanine exchange factor) which exchange GDP for GTP
• Sar-GTP undergoes conformationa change so that it inserts into cytoplasmic leaflet and start to bend the membrane
• Sec 23/ Sec 24 dimer further bends the membrane
• Sec13/31 form an outer structural cage
• disaasembly is triggered by hydrolysis of GTP bound to Sar 1

Question 11

Sec 24

Answer 11

The primary adaptor protein that interacts with the ER export signals of membrane proteins

Question 12

COPI coat is made up of a portein compelx called —- which forms —

Answer 12

• coatamer
• a thick protein coat directly on the membrane

Question 13

What bends COPI coated vesicles?

Answer 13

• Membrane bending G protein: Arf1 bound to gtp (GTP form bends membrane)

Question 14

Rretrograde transport of proteins include (2):

Answer 14

• Golgi resident proteins (trans to cis)
• ER resident proteins back to the ER

Question 15

COPI-coated vesicles retrieve ER proteins

Proteins that reside in the ER contain a —-

Answer 15

retrieval signal

Question 16

COPI-coated vesicles retrieve ER proteins

Soluble ER proteins usually contain the signals …… which is recognized by

Answer 16

• Lys-asp-glu-leu (KDEL)
• Recognized by a KDEL receptor (shuttle between cis golgi and ER compartments) interact with COPI coat

Question 17

COPI-coated vesicles retrieve ER proteins

ER membrane proteins

Answer 17

• have a retrieval signal: lys-lys-x-x (KKXX)

Question 18

Vesicle fusion steps (4)

Answer 18

1. Movement of the vesicle towards the specific target compartment. Mediated by microtubules and motor proteins
2. Tethering vesicles to the target compartment. Two types: Rod shaped/fibrious and Multiprotein complex (closer). Rabs recruit specific tethering protein
3. Docking vesicles to the target compartment. V snare put onto transport vesicles dyring budding attaches to t snare located in the target membrane
4. Fusion between vesicle and target membrane: interactions between t snare and v snare pull lipid bilayers together with enough force to cause fusion

Question 19

The ability of a vesicle to fuse to a specific membrane is determined by the specific combination of (3):

Answer 19

rabs, tethering proteins and snares