L10 Flashcards

1
Q

what can regulate exocytosis?

A

Ca2+ (calcium)

- Ca2+ regulated exocytosis found in cells specialized for secreting products rapidly on demand

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2
Q

what diseases can be due to aberrent secretion?

A
  • endocrine disorders - excess secretion of growth hormones
  • type II diabetes
  • immune disorders (high secretion of antibodies)
  • mood disorders
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3
Q

why is controlling cell secretion important?

A
  • important for maintaining cellular homoeostasis by adapting to changes in the local environment
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4
Q

what does Ca2+ have to bind to in order to trigger fusion?

A

synaptotagmin (Ca2+ sensor for transmitter release at central synapse)

-Ca2+ binds with phospholipids via the C2B domain of synaptotagmin to trigger fusion
(can bind to multiple Ca2+ ions)

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5
Q

what is the protein composition of synaptic vesicles + how was this determined?

A
  • purified neurons(+their vesicles) from the brain and did mass spectrometry
  • ~70 copies of synaptobrevin
  • synaptotagmin (Ca2+ binding sensor)
  • synaptophysin (interacts with synaptobrevin)
  • glutamate transporters
  • synapsin
  • rab proteins
  • V-ATPase

-syntaxin 1 and SNAP25 - contamination of PM

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6
Q

what does synapsin do?

A

tethers vesicles to actin cytoskeleton

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7
Q

what does V-ATPase do?

A

acidifies the inside of the vesicles

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8
Q

how many isoforms are there of synaptotagmin and how do they differ?

A
  • 16 isoforms
  • have different Ca2+ affinities
  • have different membrane/vesicle localisations
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9
Q

describe the relationship of Ca+ conc/binding to sensor and level of release/exocytosis

A
  • exponential release

- implies multiple ions are required to bind to synaptotagmin/sensor to get max/high release/exocytosis

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10
Q

Can Ca2+ bind with SNARE proteins?

A

Yes

  • Ca2+ can bind with SNARE complex which is important for the regulation of docking
  • binds with complexin which acts like a fusion clamp
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11
Q

What happens in KO synaptotagmin mouse?

A
  • released synaptic transmission not at great as in WT
  • evoked synchronised transmission is not depressed in KO
  • small amount of vesicle fusion but is unsynchronised
  • asynchronous release persists
  • hypertonic sucrose induced released - so vesicles are still being made - just not fusing
  • DOCKING DEFECT
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12
Q

WHAT DOES COMPLEXIN DO?

A

complexin clamps SNARES in a zigzag array

  • this prevents premature membrane fusion but holds SNARES in place so that they are ready for rapid synchronous fusion/release/exocytosis
  • when Ca2+ (bound to synaptotagmin)comes in it displaces complexin and allows SNARE to do final zip
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13
Q

what is synaptotagmin?

A

synaptotagmin is a major Ca2+ sensor in the membrane of presynaptic axon terminal

  • it regulates NT release
  • calcium binds to C2b domain which triggers fusion
  • synaptotagmin+calcium can displace complexin from SNARE complex - which removes clamp and allows vesicle fusion to occur
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14
Q

What ensures that only the vesicles docked near voltage gated calcium channels (VGCCs) are released by an AP?

A
  • low affinity of synaptotagmin 1,2,9
  • low affinity synaptotagmin can only sense very high calcium concentrations which only occurs when the channel is open at the mouth of the channel
  • (then calcium diffuses away rapdily
  • therefore - only vesicles docked at mouth of VGCCs undergo fusion when there is calcium influx into the cell
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15
Q

what does fast Ca2+ dependent lipsome fusion require?

A
  • the combined function of complexin II and synaptotagmin I
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16
Q

give the synaptic vesicle cycle beginning from endocytosis

A
  • during endocytosis the vesicle membrane is recovered
  • this is translocated into the cell
  • undergoes sorting
  • loaded with vesicle transporters
  • undergoes storage
  • then undergoes mobilization by actin cytoskeleton (vesicles have a motor which allows them to move along actin cytoskeleton)
  • vesicles are then cocked to the PM
  • undergo priming for vesicle release
  • calcium sensing
  • fusion - vesicle release