More membrane trafficking Flashcards
What are COPII vesicles made up of?
Sar1 GTPase
COPII coat
Carries newly synthesised proteins
What des COPI move through the golgi?
Newly synthesised proteins and retreived proteins. These are moved in an anterograde and retrograde direction
Where are proteins usually coated by clathrin
Newly made lysosomal proteins at the TGN
Most material taken up by endocytosis
Describe cranio-lenticulo-sultural dysplastia
Caused by a mutation in SEC23A, causing abnormal ER to golgi trafficking
Musculoskeletal issues
May have been issues with secretory pathway delivering collagen to the ECM
What do SEC23A and SEC24 bind to, regardless of wild type of mutant?
GTP1
How does COPII package procollagen (300-400nm)?
COPII vesicles are 60-80nm diameter
The COPII coat sorts procollagen into tubular structures which are modified for large cargo sorting
Describe the Rab family of GTPases
Member of the Ras superfamily
Cycles between membrane and cytosol
Involved in membrane and vesicular trafficking
Originally identified for being active in a vesicle-SNARE fusion
How do Rab-GTPs work in vesicles?
Recruit tethering proteins which wiggle into cytoplasm from the membrane to dock to the vesicle. This promotes SNARE assembly
What cascades allow cargo to move between organelles?
Rab cascades
Cargo moves from a Rab5 to Rab7 compartment
What can a missense of Rab7a lead to?
Charcot-Marie-Tooth 2B
Excessive activation
Reduced autophagic flux
Premature neurotrophine receptor degradation
Inhibition of neurite outgrowth
How does Legionella pneumophila utilise Rab1?
It creates an ER-like compartment
What is the role of the smooth ER
Site of lipid synthesis
Role in calcium storage
Describe the inter membrane contact site between ER and microtubules
The ER forms a loop around mitochondria with its tubules
Is there evience of the ER fusing with organelles?
No, it only has only contact sites
What is CLEM?
Correlative light and electron microscopy.
Allows fluorescence to be identified and correlated with EM.
This shows an ultrastructure not shown in light microscopy
What is tomography?
Imaging using a penetrating wave to build up 3D models of organelles.
Describe some features of membrane contact sites
Ribosomes are excluded
Membranes are very close together (10-80nm)
ER contacts can be short or long-lived
What proteins link two membranes together?
Tethers
Describe tethers
Can be protein-protein or protein-lipid
Around 30nm
Inhibit fusion
Has a defined lipid proteome
What tether transfers cholesterol?
Oxysterol binding protein (OSBP)
This is raft-like
What do tethers provide platforms for?
Calcium mobilisation
Lipid transfer
Signalling
Organelle division
How much calcium is there in the ER lumen compared to cytosol?
Cytosol- 0.1μm
ER lumen- 60-500μm
This is due to calcium taken up by the endocytic pathway
What is the Stim1 receptor?
TM calcium sensor in the ER
Monomeric under resting conditions
When calcium levels fall, Stim1 is oligomerised
What does oligomerised Stim1 interact with on the plasma membrane?
Ora1 channel
This is abundant in plasma membrane rich in PIP2
How is cholesterol moved to plasma membranes?
Cholesterol sensors in the ER switch on its synthesis. LDL receptors take cholesterol, move through the endocytic pathway and are broken down in lysosomes, releasing free cholesterol
What proteins move cholesterol through the cytosol?
Lipid transfer proteins (LTPs). Hydrophobic grooves to protect from the hydrophbic environment of the cytosol
Move along concentration gradients of lipids or ions
Describe Niemann Pick C disease
Mutation in a TM protein important in contact sites.
Lipids accumulate in spleen, liver, lungs, bone marrow and brain
Sphingomyelin accumulates in lysosomes
How are membrane contact sites involved with organelle fission?
ER surrounds fission enzymes acting on enzymes
MCSs interact these interactions
Describe 2 diseases associated with MCS
TDP-43 is linked to ALS and regulates ER-mitochondria contacts
REEP1 is associated with hereditary spastic paraplegia, leading to disruption of the ER mitochondria contacts
