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CMCB Fall > Actin > Flashcards

Actin Flashcards

1
Q

What are three types of cytoskeleton?

A
  1. Microfilaments (Actin)- usually in the cortical area
  2. Microtubules (tubulin?)
  3. Intermediate Filaments
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2
Q

what are functions of cytoskeleton?

A

cell shape, intracellular and whole cell movlemtns, for roganizling cell contents, and for integrating cells with other cells though specialized adhesions

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3
Q

What are sizes of each cytoskelton?

A

Microfilaments - Actin0 7-9 nm

Microtubules are 25 nm
-alpha and beta tubulin proteins

Intermediate filaments - 10-11 nm
IF proteins

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4
Q

what is the primary “mover and shaker” of cellular behaavior?

A

neutrophil in blood moving towards bacteria

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5
Q

what does it mean to be dyanmic

A

assembly adn disassembly

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6
Q

What is another name for atin skeleton?

A

Microfilaments

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7
Q

What part of cell is actin filametns most concentrated

A

Cortical region near the plasma membrane

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8
Q

What percent of the total protein in NON MUSCLE cells are actin?

A

5-10%

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9
Q

What % of the total protein in skeletal muscle are actin?

A

> 20%

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10
Q

How many acitn genes are in humans?

A

6>

encode different isoforms have minor differences in seuqence

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11
Q

Where are ALPHA-ACTIN present?

A

ONLY in MUSCLES

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12
Q

Where are beta and gamma actin presetn?

A

Together in no-msucle cells

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13
Q

Actin drives activity of entire cell? T/f

A

True!!! Whoel cell

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14
Q

what other specialized structures can you find actin>

A

lamellipodia, stress fibers, microvilli, others

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15
Q

what is actin called in its unassembled form?

A

G-actin (“the OG actin”

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16
Q

How big is actin

A

40-42 kilodalton globular protein

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17
Q

How many actin monomers are present/turn?

A

2 actin monomers /turn

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18
Q

where does actin monomers bind ATP?

What direction does the ……..bind? (neg or pos)?

A

Region of molecules called ATP-binding cleft

All actin subunits are going in same dirction

ATP binding cleft points to the (-) end

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19
Q

What does nucletotide binding (ATP) do to the molecule?

A

affects conformation of actin moleucel and makes it more assembly-competent

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20
Q

What is actin called once it’s polyerized

A

Filamentous or F-actin= MICROFILAMENT form

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21
Q

what conditions favor actin microfilament assembly?

A
  1. sufficient conecntration of subunits
  2. Physiological salt concentration
  3. ATP
  4. Calcium
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22
Q

Does actin form spontaneously?

A

YES!

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23
Q

The assembly of actin into MF is accompanied by delayed hydrolysis of ……

A

ATP! …atp hydrolysis is delayed with seebly of actin

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24
Q

Is energy required for assembly?

A

No!!! Assembly occurs in teh presence of non-hydrolyzing ATP Analogs

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25
Q

What is problem for cells that favor actin assembly?

A

TOO MUCH ACTIN under good conditions!

Keeping all actin fivers from assebmly into Microfilaments

restricting.directing assembly of MF to speciic cell locations

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26
Q

What are three stages of actin polymerization?

A
  1. nucleation (seeding)
  2. Elongation
  3. Steady state (equilibirum)
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27
Q

what Happens at slow nucleation/seeding stage? What is the “seed”?

A

initial lag pahse

1st few monomers to form TRIMERS OR SHORT OLIGOMERS OF ACTIN OLIGOMERS which are the “nuclei seed to contineu with elongation?

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28
Q

What is the critical concentration

A

the concentration of actin subunits at steady state equilibirium (build/diassasemle rate equilibirum)

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29
Q

Do cells use special proteins to help nucleate near filaments at specific sites?

A

Yes!

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30
Q

is the Cc changed with the addtion of a nuclei?

A

NO! not changed! just decreases lag phase

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31
Q

Is polarity more exaggerated for actin filaments or for microtubule filaments?

A

Actin filaments have a much more exaggerated polarity !

At cell

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32
Q

How fast is growth during cellular conditions for actin? plus end vs minus end

A

it is 10x fster at the plus end than the minus end!!!!

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33
Q

which end (plus or minus) is more dynamic?

A

plus end

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34
Q

how much faster does plus end grow at cellular conditions?

A

10x`

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35
Q

Can actin catalyze the hydrolysis of ATP?

A

Yes, for the fee subunits, this is extemely slow

This is delayed after actin subunits are assembled into filaments

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36
Q

Are soluble units (not polymer) T form or D form

A

T form !

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37
Q

Are polymers T form or D form?

A

It is a mixture of T form and D form!

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38
Q

Compare Critical concentration of T form Vs D form

A

Cc T form (+ end) < Cc of D form (- end)

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39
Q

Can subunits assemble when ATP bound (T form) or not bound (D for)

A

Bound!! T form

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40
Q

Where is the Energy from high energy phosphate stored?

A

In the POLYMER LATTICE.

contributes to different equilbiruim concentration (critical concentations)

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41
Q

Difference between plus end and minus end with assembly

A

As filament grows, plus end is more addtion is fastre and ATP hyrdolysis lags behind assembly, leaving cap of ATP subunits at plus end

CAP of ATP suunits at plus end b/c ATP hydrolysis lags

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42
Q

What is T forma nd what is D form ?

A

T form = subunits with bound ATP

D form- subunits without bond ATP (ADP is bound)–hydrolysis caught up

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43
Q

What is Critiical concentraiton?

A

is [x] is > Cc –> subunits are added (growing)

If [x] subunits removed (shortening)

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44
Q

What concentration does Treadmilling occur in Actin?

A

Between CC of plus and minus end

Cc(T) plus end < treadmilling < Cc (D) minus end

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45
Q

What concentration does net assembly occur

A

at high monomer concentration (concentrations above Cc D)

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46
Q

What direction (+) –> (-) or (-) –>(+) does newly added subunits move?

A

From positive (added side) to minus (removed)

47
Q

waht end/part of cell can you find actin nucleoation / (+) end location

A

Positive end Near the PM of the cell

addition of actin occursat plus ends and newly added subunts treadmill their way deeper into the cells central regions where negative sings are located

48
Q

What drugs affect actin filaments? (4)

A
  1. Phalloidin
  2. Cytochalasin
  3. Swinholide
  4. Latrunculin
49
Q

What does Phalloidin do to actin?

A

Binds and STABILIZES FILAMENTS

50
Q

What does Cytochalsasin

A

caps filament plus ends

51
Q

What does Swinholid e do?

A

Severes filaments

52
Q

Latrunculin

A

binds subunits and prevents their polymerization

53
Q

What poisons are contained in Amanita Phalloida (Death Cap Muschroom)

A
  1. Phalloidin -
    binds f-actin with high affinity
    -inhibits its depolymerization and disrupts MF function
  2. Amanita-
    attacks RNA Polymerase II 0 resulting in liver and other organ failure
54
Q

What does Phalloin do?

A

High affinity to f-actin–> prevents depolymeriastion

55
Q

What does Amanita do?

A

Attacks RNA polymeraase II –> liver and organ failure

56
Q

What are examples of non-motile actin filametns?

A

Microvilli and stress fibers (holds cells down)

57
Q

What are examples of Motile MF Assemblies

A
  1. Filopodia and Lammeliopoda

2. Contractile ring (cytoskeleton during anaphase? )

58
Q

what are actin binding proteins?

A

organize ceullular assembles of actin filaments

59
Q

What is the function of cutting/severing proteins?

A

Control lengths of Actin Filaments

60
Q

What is an example of a cutting/severing protein?

A

Gelsoilin- which is Ca Activated

61
Q

What is the function of Gelsoilin

A

Activataed by ca2+ –> attcks F-actin –> cuttign it into pieces

62
Q

What part of actin can gelsolin bind

A

2 actin bidning sites located alont eh SIDE and END of an actin filament

63
Q

What is the result of the fragmentation of actin by GELSOLIN

Does Gelsolin require Ca?

A

more “oslated” or fluid-like consistency of cytoplasm

Yes, requires ca

64
Q

what are two (loose) classes of actin cross-linking proteins

A
  1. Gel forming proteins (larger in size)

2. bundling proteis

65
Q

What is an example of a cross-linking protein

A

FILAMIN- acts as a dimer to crosslink actin fibers

66
Q

What is FILAMIN

A

dimer that crosslinks actin (actin cross-link protein)

67
Q

What kind of array does “bundling” type of actin form?

A

Parllel arrays of actin microfilaments

Can be LOOSE! Can be TIGHT!

68
Q

Example of loose bundle protein

A

Actin Filament + ALPHA- ACTININ

allows Myosin II to enter bundle (contractile bundle)

69
Q

Example of Tight Bundle

A
  • Actin Filaments + FIMBRIN!

Parallele bundle that is TIGHT! prevents Myosin II from entering bundle

70
Q

What type of proiten is found in core of Microvilli

A

FIMBRIN!!!!

71
Q

Are microvilli motile/

72
Q

What is the core of the Microvilli made from

A

Core of tightly bundld actin filaments (Dense actin filaments)

73
Q

What part of microvilli cell has positive end polarity?

A

(+) ends closest to tip of microbilli

74
Q

What is at the base of the microfilament core?

A

Terminal web@@@

contains meshwok of filaments that contains rootlets of the actin cores perpendicular actin MF, IF, and other proteins

75
Q

What is Celiac Disease? Cause?

A

Disease that damanges the SI and interferes with absorption of nutrients from food

Cause: Damaged microvilli in SI from gluten ingestion

76
Q

Cause of CD (Celiac Disease)

A

Peopel with CD cannot tolearte protein GLUTEN

Auto antibodies to actin smetimes found in CD patients

77
Q

Presentation of microvilli in CD pateints

A

Microvvilar surface (brush border) is much thinner –> decrease abosptive SA

78
Q

Why do you need adapter proteins?

A

To link actin network to PM (actin doesnt bind to any membrane protein)

79
Q

membrane ADapter proteins for platelet?

A

FILAMIN

Filamin links MF to Glycoprotein complex in membrane

80
Q

Filamin vs Fimbrin

A

Filamin- adapter protein for platelets

Fimbrin- cross linking protein taht result in tight bundles of actin - Fimbrin found in core of microvillus

81
Q

What is membrane Adapter protein in Muscle Cell?

A

DYSTRPHIN-

attracks actin filament to integral glycoprotein complexes

82
Q

What doe s defect in Dystrophin Gene Cause?

A

Duchemme’s Muscle Dystrophy

Fatal

83
Q

proteins in apical membrane of various epithelial cells are linked to actin MF by what?

A

ERM family of proteisn
(Erzin, Radizin Moesin)

direclty or through intermediate proteins such as EBP50 or CFTR prtoein (Cystic fibrosis TM conductance regulator protein

84
Q

What is the major protein that provides structural basis for cortical cytoskeleton in RBCs

A
  1. Actin Binding Proteins SPECTRIN (dimer)

undertneath PM

Takes a lot of abuse

85
Q

What does the RBC elaborate cortical cystoskeleton consist f?

A

Spectrin
Actin
Adaptors

86
Q

What is the structure of Spectrin

A

Long Alpha and Beta Chains associated laterally to form DIMERS then Tetramers with actin binding domains at both sides

87
Q

What do ends of spectrin TETRAMERS bind to?

A

Short Actin Filaments

88
Q

What is protein ANKYRIN

A

Ankyrin binds to spectrin and TM proteinBadne 3

89
Q

What are Protein 4.1 binds to ?

A

Protein 4.1 binds to spectrin-actin jucntions and to Glycophorin, an abundant TM protein

90
Q

What is the problem with solutlbe monomer concentrations of actin?

A

High in cells

Problem keepign them from polymerizing

91
Q

Solution to polyermizations

A

Seqeunstering monomeric actin using special actin binding proteins

Thymosin and Pofillin

92
Q

what are the most abundant sequestering proteins?

A

Thymosin- locks actin monomers cannot assempt

93
Q

What is profillin?

A

Competes with thymosin for actin monomer

Prifllin actin dimers can readilya dd to actin filametns

Adds to face of actin OPPSOITE the ATP bnidng cleft (which is on teh minus end)

Cannot bind to minus end of actin ,but easily adds to positive end

94
Q

How to you “activate” profillin ?

A

By Phosphorylation and inositol phospholipid binding (IP3)

95
Q

What is result of locally activating profilllin

A

movment of actin from the seqeunstered thymosin pool into an ASSEMBLY Pool

Actin moves from sequenstered pool –> Assembly pool

96
Q

Fucntion of Formin Proteins?

A

large family of Actin Binding PRoteins taht fomrs Dimeric Complex–> NUCLEATES new actin filaments –> elongates

97
Q

hat are ends of Formin protein associated with?

A

Rapidly growing postive ends of actin filaments as they elongate

98
Q

What are “whiskers”

A

contain binding sites for profillin or the Profiln- Actin Dimers (Right side)

Serve as “stagin area” to inrease rate of actin filametn elongation

99
Q

Formin protein fucntion? What doe formin proteins typically nucleate?

A

Nucleats growth of striaght, unbranched filaments whih link into parallel bundles (unlike ARP mediated actin webs)

100
Q

What is an ARP?

A

Actin Related Protein complex

101
Q

What is the structure and functino of ARP

A

ARP 2 and ARP 3 have a strcuture similar to actin monomer but unable to form filaments on their own (not spontaneous)

102
Q

Can ARP form filaments on their own?

103
Q

What happens when they are activated

A

Forms a complex that mimics the plus end of MF

simulates NUCLEATIOn and growt of new actin filaments

104
Q

What is the result and end product /structure of ARP activation

A

Bc of unique binding of ARP complexes to the sides of existing filaments wit a particular configuartion, a web of actin branches form from existing filaments

105
Q

Difference betwen the nucleation caused by Formin proteins and the Nucleation caused by ARP proteins

A

Formin protein nucleation- strainght unbranched filaments (actin filaments can sponaneously grow)

ARP proteins- similar sructure to actin monomer, nuclates to form a WEB of actin BRANCHING from existing filaments

70 degre branches

106
Q

Where is nucleation by ARP mediated at?

A

Leading Edge

107
Q

what angle are newly nucleated actin filmants attached

A

70 degrees to side of pre existing filament

108
Q

What is cofillin?

A

Destabilizes Actin Filament (it’s an actin filaminet binding protein)

109
Q

What makes Cofillin unusual?

A

It binds to both filament and globular forms of actin

110
Q

What form of actino for Cofillin prefer?

A

ADP containign actin filaments (older filaments)

111
Q

What does binding to COfillin do?

A

Makes it easier for ADP actin to dissociate from minus end

112
Q

Overall

A

Enables actin filaemnt entowrk as a whole to move forward, pushing out leading edge of a moving cell

113
Q

How does cell walk i.e. lamellooodeim

A
  1. extention/protrusion (actin polymerization)
  2. movement of unpolymerized actin–> forms translaocation
  3. Detarchmentand contraction of trailing bak end
  4. Afoward movment (actin myosin interaction)

CMCB Fall (17 decks)

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