Protein Phosphatases Flashcards

1
Q

Is the protein kinase reaction reversible or irreversible?

A

Irreversible, protein phosphatases induce a different reaction, hydrolysis

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2
Q

Why is phosphorylation irreversible?

A

Since it produces ATP and hydrolysis by protein phosphatases does not

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3
Q

What is a phosphorylase?

A

Causes phosphorylation of a substrate

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4
Q

What is phosphorylase kinase?

A

Phosphorylates the phosphorylase

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5
Q

What is PP1

A

Phosphorylase phosphatase - dephosphorylates phosphorylase

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6
Q

How is Src activated?

A

Dephosphorylation of pTyr508

Phosphorylation of Tyr397

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7
Q

How many kinases are in the kinome?

A

> 500

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8
Q

How are kinases and phosphatases families different?

A

Most kinases are similar, phosphatases are different based on their catalytic mechanisms and amino acid sequences

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9
Q

How many phosphatase phynogenic trees are there?

A

10

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10
Q

What family due tyrosine phosphatases belong to?

A

CC1

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11
Q

What are dual specificity phosphatases?

A

They can be serine/threonine phosphatases or tyrosine phosphatases

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12
Q

Which dual specificity phosphatase is different and why?

A

PTEN

It can be a lipid or protein tyrosine phosphatase

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13
Q

What do phosphatases recognise?

A

Molecular features instead of consenus sequences around the phosphorylated site

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14
Q

What is the difference between protein tyrosine phosphatase catalytic pockets to serine/threonine phosphatases?

A

Tyrosine phosphatase catalytic pockets are deeper than serine/threonine phosphatase catalytic pockets

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15
Q

Why do tyrosine phosphatases have deeper catalytic pockets than serine/threonine phosphatases?

A

Phospho-tyrosine is a big molecule

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16
Q

Describe the active site of PP1

A
Contains a bimetal centre 
Bridged by a water molecule, which is displaced by the binding of phosphate 
Has 3 grooves:
- an acidic groove 
- a C-terminal groove 
- a hydrophobic groove
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17
Q

What is the mechanism of the phosphate in PP1?

A

The phosphate undergoes nucleophilic attack by a hydroxyl ion
Histidine125 provides a proton to the alcohol group
Metal ions are important in coordinating this mechanism

18
Q

What is the inhibitor of PP1?

A

Inhibitor 1 and 2

19
Q

What is the inhibitor of PP2A?

A

Okadaic acid

20
Q

What is the inhibitor of PP2B?

A

Trifluoperazine

21
Q

What is the inhibitor of PP2C?

22
Q

What is the activator of PP2B?

A

Ca2+-calmodulin

23
Q

What is the activator of PP2C?

24
Q

Where is PP2B abundant?

A

In the brain

25
What does EDTA do?
Collates magnesium ions and inhibits them
26
What causes diuretic shellfish poisoning?
Okadaic acid
27
What does blue-green algae produce?
Microcystin
28
Where does microcystin bind covalently to of PP1, PP2A and related PPP enzymes?
A cysteine residue in the beta12-13 loop
29
What happens if you add toxins to paramecium? and why?
They swim backwards A calcium pump regulates the directionality of the flagella, if this is blocked in the phosphorylated state then it jams the flagella in terms of directionality
30
Name some physiological processes involved in PP1 signalling
``` Glycogen metabolism Muscle contractility Protein synthesis Ca2+ uptake by SR Cell division cycle ```
31
What are the substrates for PP1 for glycogen metabolism?
Glycogen phosphorylase | Glycogen synthase
32
If PP1 is involved in so many cellular processes, how are these processes regulated so specifically?
The catalytic subunits of PP1 are bound to various location by different targeting or regulatory subunits
33
How do you prepare microcystin-sepharose for affinity chromatography?
The O in microcystin makes the carbon slightly electropositive The S in sepharose can give a negative charge which attacks the carbon Forms a covalent bond between sulphur and carbon
34
What does dephosphorylation of myosin regulatory light chain cause?
Smooth muscle cell relaxation
35
What happens when PP1C is blocked in the gut by okadaic acid?
Smooth muscle in the gut contacts
36
What happens when PP1C interacts with regulatory subunit MYPT1?
It makes PP1C better at desphosphorylating myosin light chains than on its own as it provides a bigger platform for interaction with the substrate
37
What is the two functions of MYPT1?
Brings PP1C to the mysin | Acts as a platform which enhances the phosphatase specificity
38
What is MYPT1?
A myosin regulatory subunit
39
How does myosin light chian interact with PP1C?
The arginine and lysine of the mysoin light chain interact with the negatively charged acidic groove
40
What is a common motif in most regulatory subunits of PP1?
RVxF/W
41
In response to adrenalin, what does PKA phosphorylate? What effects to these have?
``` Glycogen synthase (inhibits it) - reduce glycogen synthesis Phosphorylate phosphorylase kinase (activates) - increase glycogen breakdown Site 1 and 2 of glycogen-binding subunit - PP1c cannot bind to glycogen-binding subunit - translocates to the cytoplasm Inhibitor 1 (activates) - inhibitor 1 inhibits PP1c in the cytoplasm ```
42
What is the function of targeting subunits of PP1?
Targeting or localisation - bring the phosphatase to the substrate Alter substrate specificity Regulation of PP1 activity