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BISC 428 > Lecture 13 > Flashcards

Lecture 13 Flashcards

1
Q

How do things move?

A

1) Cytoskeleton as tracks for motor proteins
2) Cytoskeleton for movement (actin filaments, microtubules)
3) Brownian Motion

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2
Q

What are the 2 cytoskeletal elements that are used as track because they are POLAR filaments?

A

Actin filaments (Myosin)
Microtubules (Kinesis, Dynein)

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3
Q

What is most intracellular movement in ANIMAL CELLS due to?

A

It is due to material moving along microtubules

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4
Q

What is most intracellular movement in PLANTS and FUNGI due to?

A

It is due to material moving along actin filaments

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5
Q

What do all molecular motors have in common?

A

Use ATP for their movement
Have 2 parts (a motor domain [Head] and a tail), they are usually linked together by a neck (AKA. neck-linker)

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6
Q

What is a motor domain?

A

Uses ATP hydrolysis to move the motor

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7
Q

What is a tail?

A

Binds to cargo and can bind to other parts of the motor to inhibit the motors function when not in use

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8
Q

What will happen to the cytoskeletal element if a motor is anchored in position?

A

Then the cytoskeletal element will physically move when the motor is activated

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9
Q

What will happen to the motor if the cytoskeletal element is anchored in position?

A

Then the motor will physically move when the motor is activated

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10
Q

What are the only molecular motors that use actin as tracks?

A

Myosin

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11
Q

Which way does myosin move?

A

Usually moves towards the barbed end (+ end) of actin filaments… only 1 moves towards the - (pointed end)

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12
Q

What does myosin use for movement?

A

An ATPase. Uses ATP for movement

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13
Q

How many heads can myosin have?

A

Can have 1 or 2 heads, which are the motor domains

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14
Q

What are the heavy chain components of the head?

A

1) Binds and hydrolyzes ATP
2) Binds to Actin filaments

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15
Q

What are the light chain components of the head?

A

There are about 1 to 7 of them depending on the myosin
Activate the myosin in the presence of Ca2+

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16
Q

What does myosin attach to?

A

It attaches to many types of tails

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17
Q

Where were myosins discovered in?

A

They were discovered in skeletal muscle

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18
Q

What do muscle myosins do?

A

It creates the force for skeletal muscle contraction

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19
Q

How many binding sites are activated during normal muscle contraction?

A

Only 10-20%

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20
Q

What is muscle myosin called?

A

Myosin II

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21
Q

How many heads does Myosin have?

A

Has 2 heads attached to a long coiled-coli tail that intertwines.
These are called the thick filaments (in skeletal muscle).
The 2 strands of actin filaments that they bind to are called the thin filaments.

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22
Q

What terminal of amino acids forms the globular catalytic domain?

A

The N-terminal 710 amino acids form the globular catalytic domain.

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23
Q

Where does ATP dock into?

A

ATP docks into the nucleotide binding site of the molecule

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24
Q

Where does Actin bind?

A

Actin binds ~4 nm away from the ATP on the other side of the head

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25
Q

What does the globular head bind to?

A

The globular heads bind tightly to actin in the ABSENSE of ATP. This causes rigor mortis (no ATP produced when dead). Nearly 100% of binding sites are triggered during rigor. The heads only release in the presence of ATP.

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26
Q

What happens when heads are isolated?

A

When heads are isolated and used for actin experiments they bind to the filaments forming arrow-head shapes. This indicated the pointed and barbed ends of the actin filament.

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27
Q

What does myosin bind to?

A

Myosin binds to 2 adjacent actin subunits within the actin filaments

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28
Q

What are sarcomeres?

A

The structural unit of actin (thin filaments) and myosin (thick filaments) in skeletal muscles are called sarcomere

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29
Q

Are there also cytoplasmic Myosin II’s in the general class of Myosin II proteins?

A

Yes

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30
Q

What are thick filaments called?

A

Muscles (Myosin II)

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31
Q

What are thin filaments?

A

Actin filaments

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32
Q

How many classes are there are the Myosin superfamily?

A

35 classes (so far in eukaryotes)

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33
Q

How many motors are “orphans” that don’t fall into those classes?

A

145

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34
Q

How many organisms have the genes from all classes?

A

No organism has the genes from all classes, onlt a subset of classes

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35
Q

How many myosin genes and classes do humans have?

A

Humans have 40 myosin genes from 13 classes

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36
Q

Where did Myosin originate from?

A

All originated from a gene similar to Myosin I, but plants have lost Myosin 1.

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37
Q

What did that gene then originate?

A

The gene then originated the Myosin V gene

38
Q

What do diverse tails give?

A

Diverse tails give myosins their specificites for different cargo

39
Q

What are some ways that myosin got their diversity?

A

Gene duplication
Acquired extra domains
Evolutionary Divergence (Got divergent tails to bind to different cargos)

40
Q

What is the first unconventional myosin discovered?

A

Myosin 1

41
Q

What are heavy chains encoded by in Myosin 1?

A

8 genes

42
Q

What Myosin group has a very diverse class of Myosins, large in number?

A

Myosin 1

43
Q

How many heads does Myosin 1 have?

A

Only have 1 head, so many must work together for movement, but 1 must always remian attached to the actin filament so they don’t fall off

44
Q

How many light chains are in Myosin 1?

A

Variable number of light chains can associate with them

45
Q

Is there a head and tails association in Myosin 1?

A

The heads don’t really associate with the tials, so they have very short tails.

46
Q

What kind of domains do Myosin 1 have?

A

Have odd domains including:
1) A basic domain that binds to acidic phospholipids
2) SH3 (src homology-3) domain to bind to proline-rich areas of other proteins

46
Q

What kind of domains do Myosin 1 have?

A

Have odd domains including:
1) A basic domain that binds to acidic phospholipids
2) SH3 (src homology-3) domain to bind to proline-rich areas of other proteins

47
Q

What engulfing process is Myosin 1 involved in?

A

Involved in endocytosis (it is normally concentrated at sites of phagocytosis and macropinocytosis)

48
Q

How does Myosin 1 function in linking two things together?

A

It links the actin of microvilli to the membrane

49
Q

What is the structure of the chain in Myosin V?

A

Has a very long light chain domain
1) This allows it to take very long (36 nm) steps along the actin filaments
2) When only 1 head was labeled with a fluorescent probe, 72 nm movements were detected

50
Q

What does Myosin V transport?

A

Pigment granules, ribonucleic proteins, mRNAS, enzymes

51
Q

What are the most processive motors to date?

A

Myosin V. It can take multiple steps without falling off of the actin filaments).
One head binds before the other releases.

52
Q

What does the gene for Myosin V give rise to?

A

The gene for Myosin V gave rise to Myosins VIII and IX

53
Q

Do Myosins V, VIII, and IX move slow or fast?

A

They move very fast

54
Q

What do defects in Myosin V cause?

A

Seizures
Gricelli’s syndrome (a recessive human disease of pigmentation dilution)
Immunodeficiencies

55
Q

What happens when the Myosin V motor is not in use?

A

When not in use the motor folds up on itself. The tail interacts with the head

56
Q

What is the only myosin to move to the pointed (-) ends of actin filaments?

A

Myosin VI

57
Q

What causes this movement in Myosin VI?

A

Caused by the lever arm naturally swinging in the opposite direction as other myosins. Myosin VI is an actin-based motor that moves backwards.

58
Q

Is Myosin VI a monomer?

A

It is a monomer, but adaptor proteins can dimerize it, allowing for large 30nm steps.

59
Q

How does Myosin VI relate to vesicles?

A

Can move vesicales from the plasma membrane into the cytoplasm during endocytosis.

60
Q

What do mutations in human Myosin VIIa (7a) cause?

A

Mutations cause deafness at birth, then retinal degeneration, which leads to blindness

61
Q

Is Myosin VIIa a monomer?

A

It is a monomer, but can dimerize. When dimerized in vitro and in vitro, it is processive but it is very slow. This hasn’t been shown in vivo yet.

62
Q

Are there cargo receptors in Myosin VIIa?

A

No cargo receptors have been identified

63
Q

What is the function of Myosin VIIa?

A

Unknown, but it moves so slowly that some researchers think it might act as a structural myosin, bundling actin filaments together.
Others think it could act as a molecular force sensor.
(It would stall when forces became too strong when moving along actin filaments)

64
Q

What is Myosin 18A?

A

Has multiple spliced forms and differing subcellular localizations

65
Q

How is Myosin 18A similar to Myosin II?

A

It’s core (coiled coil domain) is most similar to Myosin II, but it is still quite divergent.

66
Q

What is the IQ domain in Myosin 18A?

A

IQ domain: where the light chains bind (very small domain)

67
Q

What is the PDZ domain in Myosin 18A?

A

Has an amino-terminal PDZ domain (usually used for protein protein interactions). This is unique to this myosin. No other myosins have PDZ domains (large domain)

68
Q

What is the KE motif in Myosin 18A?

A

KE motif: Lysine-Glutamic acid repeat region (unknown function)

69
Q

What do many post-translational modifications get in Myosin 18A and actin?

A

Gets Tyrosine, Serine, Threonine phosphorylated, ubiquitylated, acetylated, methylated (largely based on proteomics screens). These modifications have unknown functions on the protein

70
Q

What is Myosin 18A and actin involved in?

A

Is involved in the retrograde treadmilling of actin. Has been found as part of protein complexes

71
Q

What did immunoprecipitations find in the binding in a complex in Myosin 18A and actin?

A

Immunoprecipitations found MYO18A Myotonic dystrophy kinase-related CDC42-binding kinase (MRCK) and Leucine-rich adaptor protein 1 (LURAP1) binding in a complex

72
Q

What does LURAP link in Myosin 18A?

A

LURAP links MRCK to MYO18A

73
Q

What can MRCK do to MYO18A?

A

MRCK can phosphorylate MYO18A

74
Q

What does MRCK phosphorylating MYO18A lead to?

A

1) This leads to increased cellular protrusions
2) This complex is involved in the retrograde flow of the actin-myosin complexes at lamellipodia and the center of the cell

75
Q

Is Myosin 18A a motor?

A

Myosins usually bind to actin through their motor domains. There is no interaction of the Myosin 18A motor domain and actin, even with ATP depleted (Note: ATP depletion causes very strong binding of myosins to actin in other systems)

76
Q

Is there a connection between MYO18A and actin?

A

MYO18A and actin do bind between the KE and PDZ domains at the N-terminus.

77
Q

What cannot hydrolyze ATP at all?

A

Drosophola Myosin 18A (called Mhcl, Myosin heavy chain-like) cannot hydrolyze ATP at all

78
Q

What can hydrolyze ATP weakly?

A

Mouse Myosin 18A can only weakly hydrolyze ATP from its light chains and binds only weakly to actin.

79
Q

What is the target and mechanism of blebbistatin?

A

Target: Myosin II
Mechanism: Hinders Pi release

80
Q

What is the target and mechanism of BTS?

A

Target: Myosin II
Mechanism: Hinders Pi release and ADP release

81
Q

What is the target and mechanism of BDM?

A

Target: Myosin II
Mechanism: Hinders Pi release

82
Q

What is the target and mechanism of PCIP?

A

Target: Myosin I
Mechanism: Reduces coupling between actin and nucleotide binding sites

83
Q

What is the target and mechanism of PBP?

A

Target: Myosin V
Mechanism: Reduces ADP dissociation, ATP binding/hydrolysis, and coupling between actin, nucleotide binding sites.

84
Q

How often is the cell cortex under tension?

A

The cell cortex is ALWAYS under tension

85
Q

What generates the tension in the cell cortex?

A

Non-muscle myosin-2 genereates the most cortical contractile tension

86
Q

How does non-muscle myosin-2 generate the most cortical contractile tension?

A

Through pulling on actin filaments at the cell cortex, this leads to stress in the cortical actin network, which then leads to stress at the membrane. Myosin-2 does this by generating bipolar minifilaments at the cell cortex

87
Q

How many heavy chain isoforms are there?

A

There are 3 non-muscle myosin-2 heavy chain isoforms

88
Q

What do all 3 non-muscle myosin-2 heavy chain isoforms localize to?

A

They all localize to the cell cortex (Myosin-2A, -2B, -2C)

89
Q

What do these isoforms do?

A

These isoforms can co-assemble into mixed minifilamemts too

90
Q

What does Myosin-1 do?

A

Myosin-1 also binds actin to the membrane at the cell cortex as does Myosin-18. These can all co-assemble with non-myscle Myosin-2 at the cortex.

BISC 428 (23 decks)

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