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Membrane_dynamics Flashcards

1
Q

Three aspects of membrane dynamics

A

Membrane fusion, fission, and curvature

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2
Q

Three classes of membrane fusion and an example of each

A

Cell-cell fusion (sperm-egg), host-pathogen (viral infection) and intracellular fusion (neurosecretion/exo-endo cytosis)

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3
Q

Steps in membrane fusion (4)

A
  1. Adhesion (targeting)
  2. Stalk intermediate
  3. Hemifusion
  4. Fusion pore (opening)
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4
Q

How are different stages of membrane fusion assayed? (2)

A

Content dye, lipid markers

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5
Q

What dictates specificity during membrane fusion?

A

For viruses- HA1, binds to sialic acid on host cell

For vesicles - Rab GTPases, tethers, SNAREs

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6
Q

Methods to study fusion

A
  1. Mixing of fluorescent dyes

2.

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7
Q

How is the repulsive force of the two bilayers overcome?

A
  1. By the force of fusogenic proteins and their interacting factors (ie SNAREs and NSF/SM/SNAP)
  2. Charge gradient?
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8
Q

What is the nature of the hole that opens between the two bilayers?

A

Up for debate - whether it is formed by lipids only, lipids+SNAREs, more study needed

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9
Q

How is membrane fusion regulated?

A

In neurosecretion - Ca and Ca binding proteins, activates docked synaptic vesicles
Could also be fusion protein modification, synthesis or degradation, or protein targeting

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10
Q

What defines influenza virus subtype?

A

HA fusion protein

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11
Q

Is pH within endosomes very high or very low, or in between?

A

Very low

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12
Q

What environmental factor triggers HA conformational change?

A

pH change, allows for extension of coiled coil structure

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13
Q

HIV entry mechanism

A

Attaches to CD4, binds chemokine receptor, membrane insertion, conformational change, fusion, and entry of viral nucleocapsid

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14
Q

Antiviral drug strategy for HIV (enfuvirtide)

A

Hairpin inhibitor that prevents conformational change of fusion proteins

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15
Q

Two types of SNARES and an example of each

A

T-SNARES (target membrane)
- syntaxin
V-SNARES (vesicle)
- VAMP

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16
Q

Proteins that help SNAREs drive membrane fusion

A

NSF (chaperone), SNAP (soluble NSF attachment, (SM)

17
Q

What structure do SNAREs form between vesicle and target membrane

A

stable 4-helix bundles (parallel coiled coil)

18
Q

How was it shown that SNAREs are sufficient to drive fusion?

A

reconstitute SNAREs into liposomes and examine fusion by de-quenching

19
Q

Issue with in-vitro SNARE reconstitution

A

Needed a super high concentration in order to do anything, which is how people identified a positive regulator of SNARE action - SM proteins

20
Q

Mechanism of SM action

A

Form stable complex with SNARE complex, push reaction forward to drive membrane fusion even at high concentration

21
Q

Difference between cis and trans-SNARE complexes

A

cis-SNARE conformation exists after membrane fusion, no force applied
trans-SNARE exert inward force in order to create pore

22
Q

Recycling factors for future rounds of membrane fusion

A

NSF / SNAP (? - double check this)

23
Q

hemifusion

A

lipid mixing but not content mixing

24
Q

Function of NSF chaperone and SNAP

A

disassembly of SNARE complex

25
Q

What are diff types of membrane division? (4)

A

Cell division, intracellular vesicles pinching off, organelle division, formation of multi-vesicular bodies

26
Q

Two classes of membrane fission mechanisms and an example of when you see them

A

Pinch from outside (dynamin-related GTPase driven during mito division)
Pull from inside (actin/myosin filaments of contractile ring in cytokinesis)

27
Q

What is the role of dynamin in endocytosis

A

Assembles onto neck of fusion pore created by plasma membrane invaginations, squeezes (powered by GTPase) to release vesicle

28
Q

Does dynamin function as a “pinchase” or a “poppase”

29
Q

What protein group mediates division/fusion of mitos

A

Dynamin-related GTPases (DRPs)

30
Q

ESCRT

A
  • membrane budding and fission complex, important with multi-vesicular body formation, cytokinesis, and viral budding
  • sufficient for formation of intraluminal vesciles
31
Q

Three ways in which vesicles can be formed

A

Filament assembly
Protein conf change
GTP hydrolysis

32
Q

Different phospholipid shapes largely driven by (3)

A
  • Size of head group
  • Number of fatty acid chains
  • Shape of fatty acid chains (dependent on saturation state)
33
Q

Negative curvature dominated by what shaped lipids

A

cone-shaped

34
Q

Enzymes that can change shape of lipids

A

phospholipase (alter), acyl transferases (invert)

35
Q

Ways to curve a membrane (5)

A
  1. Insert small protein in one side of membrane
  2. Scaffold membrane
  3. Lipid composition
  4. Transmembrane proteins
  5. Cytoskeleton

CSD (13 decks)

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