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ANAT 212 > Lecture 13 > Flashcards

Lecture 13 Flashcards

1
Q

describe vesicle traffic

A

Multiple donor and acceptor (target) membranes in secretory pathway
Two mechanisms ensure that vesicles transport their contents to the correct acceptor membrane

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2
Q

name the 2 mechanisms for vesicle traffic

A

Rab GTPase proteins provide specificity of vesicle targeting and attachment to acceptor membrane (Traffic 2)
SNARE fusion proteins provide specificity during fusion of vesicles with acceptor membrane (Traffic 3)

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3
Q

why multiple steps in secretory pathway to the golgi apparatus

A

if mistake= cannot repair, can go one step back
many ptms providing functions

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4
Q

describe transport through golgi

A

golgi organized into stack of membranes = cis (closer to er), medial (middle), trans (closer to pm)
3 models
cytosolic protein matrix maintains organization of stack

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5
Q

describe transport through golgi - old model

A

Vesicles transport cargo between layers
cis–>trans–>membrane binds cop2

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6
Q

describe transport through golgi - new model

A

each layer matures and becomes next layer
no cop2 vesicles
each compartment matures to next
golgi resident proteins are carried backwards by COP1 vesicles
clathrin coated vesicles carry cargo to pm and endosomes

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7
Q

describe glycosylation in golgi

A

N-linked glycans are modified by removal of mannoses and addition of different sugars, often with negative charge
Other complex oligosaccharides are attached to Ser and Thr side chains – O-linked glycosylation
Many final combinations of oligosaccharides – heterogeneity

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8
Q

describe glycosylation in golgi generally

A

diff from er
gives specificity
can modify mannoses, polyglycans, many diff combos, diff types of glycans added
sugar - makes protein more soluble so no aggregation, acts as coat - prevents from degradation
rich in OH so as progress = diff combos of signalling pathways
helps proteins fold properly

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9
Q

what are the functions of glycosylation in the golgi

A

promotes protein folding
Sugars have limited flexibility ->Protects from proteases, stabilizes protein structure (protective coat)
Signaling hubs (regulation of development

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10
Q

describe how glycosylation in golgi promotes protein folding

A

Makes folding intermediates more soluble (prevents aggregation)
Sequential modifications -> Glyco-code ->Progression folding or degradatio

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11
Q

describe modifications in the golgi - proprotein convertases

A

som pm and extracellular proteins are made as longer inactive form at the er, then cut by proprotein convertases into a shorter, active form at the golgi
proteases recognize specific patterns of aas - endonucleolytic cleavage and liberates active part of protein
cleavage often activates proteins by removing inhibitory region

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12
Q

give ex of proprotein convertases

A

proinsulin is made as one inactive polypeptide
convertases remove middle section, then 2 remaining sections form active insulin
prevents premature signalling by insulin at the er
brings N and c terminus together
when stimulus = cuts proteins
middle acts as repressor
no specific motifs but some combos recognized better
makes disulfide bonds when passes through er

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13
Q

give ex of regulation by proteases

A

protein cleaved in golgi - upr
golgi signal usually hidden by chaperones
n terminus of protein = active transcription site
ATF6 is activated by convertase proteolysis in the Golgi
Regulation is by trafficking= BiP covers ER exit signal on ATF6 and proteases are only in Golgi

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14
Q

how does rab gtpase work

A

works same as ras
when active = anchored through 2 prenyl groups - anchored into membrane

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15
Q

describe rab proteins

A

Large subfamily of Ras-related proteins
Different organelles and vesicle types in secretory pathway have unique sets of Rab proteins
Switched “on” by GEF, “off” by GAP
Rab-GTP binds to a large number of Rab-effector proteins which mediate vesicle targeting

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16
Q

name rab functions

A

act at several steps in vesicle targetting
assist cargo selection and coat formation during vesicle budding
connect vesicle to motors on cytoskeleton for transport
tether vesicles to acceptor membrane - specificity
does many things, but other components = cofactors
Recognize cargo
transport, tethering, fusion

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17
Q

describe rab membrane anchor

A

Rabs have two prenyl lipid groups attached at their C-termini

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18
Q

describe rab in gdp bound state

A

In the GDP-bound state, Rab is soluble and not associated with the membrane
lipid is covered up by other proteins (GDI,GDF)
to hide them (prenyl groups)

19
Q

describe rab in gtp bound state

A

In the GTP-bound state, the lipid modifications are exposed and anchor Rab to the membrane
theRab-effector proteins become attached to the membrane through Rab-GTP
sometimes has amphiphatic hexlix - stronger, tighter

20
Q

describe rab activation

A

Specific GEF on membrane produces anchored, active Rab-GTP= GEF is linked to formation of vesicle coat
rab gtp works through effector proteins

21
Q

describe how rab gtp works through effector proteins

A

attach vesicle to motor proteins
tether vesicle to target membrane
activate PI kinases and GEFs to make more Rab-GTP in clusters on acceptor membrane

22
Q

describe 4 steps of vesicle rab cycle

A
  1. Vesicle Rab is activated by
    GEF on donor membrane and packaged onto vesicles- some interact with cargo, assist uncoating, or attach to motors
  2. Vesicle Rab-GTP binds specifically to tethers on acceptor membrane
  3. After fusion,GAPs on target membrane inactivate Rab
  4. Inactive vesicle Rab-GDP is recycled through cytosol to donor membrane
23
Q

describe cytoskeleton

A

protein filaments - actin - and microtubules - tubulin - run through cytosol and provide structure to cells
vesicles travel with molecular models
connected to each other and anchored to organelles and pm (cortical skeleton)
usually localized in specific places, like in synapses for neurons, for microtubules = long so goes from nucleus to end of cell

24
Q

describe actin filaments

A

shorter
often clusteres at pm
highly cross linked into network
motor = mysosins

25
Q

describe microtubules

A

motor = kinesins and dynines
longer, thicker organized around centrosome near nucleus

26
Q

describe motor protein transport

A

Motor proteins transport vesicles along cytoskeleton= myosins on actin, dyneins and kinesins on microtubules, different families and mechanisms, but all are ATP-dependent
Motors themselves do not provide targeting specificity, but bring vesicle to general location of acceptor membrane
rabs tell where to go

27
Q

what are many rab effectors

A

tethers = long proteins which connect vesicle with acceptor

28
Q

describe tethers

A

bound to a specific vesicle rab on one end, and a specific membrane site on the other end - the site on acceptor membrane = rab in some cases and diff in others
arm bends and gets closer to membrane and fuses
tethers = first determinant of vesicle targeting specificity

29
Q

describe types of tethers

A

Tethers of different structural families act at different organelles
Coiled-coil tethers mostly within the Golgi and on endosomes
* Multisubunit tethers act at other compartments= ER to/from Golgi, Golgi to PM, Endosome and lysosome

30
Q

describe coiled coil tethers

A

Dimers with coiled-coil structures (pairs of α-helices) that remain assembled after use
Coiled-coil tethers form the Golgi matrix

31
Q

describe how coiled coil tethers form golgi matrix

A

maintain the organization of the Golgi stack=
connect vesicles to Golgi
anchored to membrane, or attached by GTPases
long filaments with multiple Rab bindingsites
mainly works in golgi
recognizes site so then vesicle trapped and fuses

32
Q

describe multisubunit tethers

A

most secretory pathway steps involve multisubunit tethers

33
Q

name types of diff structural families of multisubunit tethers

A

ER to Golgi, within Golgi (TRAPPI, II)
endosome and lysosome (HOPS/CORVET)
ER and PM: CATCHR family (exocyst, GARP, COG, Dsl1)

34
Q

describe ER to golgi (TRAPPI) - gen

A

TRAPP1 works well with coiled coil tether
gef = brings rab gtp = now needs effector
ine rab attached to membrane = interacts with coiled coil tether
Identifies vesicle attached to 115 and that attached to rab
conformational change in coil coiled tether = bends and brings vesicle closer to recognition domain once attached = interact with snares to fuse protein

35
Q

describe ER to golgi (TRAPPI) - 4 steps

A
  1. TRAPPI acts as GEF for Rab1 on Golgi
  2. Rab1 binds coiled-coil tether
  3. CC tether binds to vesicle and hands vesicle to TRAPPI, closer to membrane
  4. TRAPPI helps organize SNAREs
36
Q

name domains of TRAPPI

A

3 domains = vesicle recognition, GEF, SNAREs

37
Q

name steps of exocyst at PM (CATCHR family) - 3

A
  1. Before tethering but after uncoating, some subunits are on either vesicle or PM
  2. Complete 8-mer complex forms tether
  3. May bring SNARE to membrane to start fusion
38
Q

what does rab 1 do

A

er to golgi

39
Q

what does rab 2 do

A

golgi to er

40
Q

what does rab 7 and rab 9 do

A

golgi and early to late endosome

41
Q

what does rab 5 do

A

endocytosis from pm to endosome

42
Q

what does rab 4 and rab 11 do

A

recycling from endosome to pm

43
Q

what does rab 3 do

A

exocytosis of secretory vesicles

ANAT 212 (34 decks)

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