Metalloproteins - Calcium

Question 1

Describe calcium signaling and calcium activation.

Answer 1

pg 7

Question 2

What part of the Voltage Gated Calcium Channel (VGCC) does calmodulin (CaM) bind to, and what does it do?

Answer 2

CaM (Calcium-calmodulin) binds to the C-terminal of the cytoplasmic domain of the alpha 1 subunit.

Question 3

What is one part of the VGCC which the beta subunit binds to?

Answer 3

The AID (alpha interaction domain) it is on the I - II loop

Question 4

What is calcium-calmodulin’s effect on PMCA (Plasma membrane calcium -ATPase)?

Answer 4

It activates them.

Question 5

What two subunits of the VGCC can be phosphorylated?

Answer 5

• Alpha 1
• Beta

Question 6

Where is CLSQ (Calsequestrin) located?

Answer 6

in the sarcoplasmic/ endoplasmic reticulum

Question 7

Roughly how many target proteins does calmodulin have?

Answer 7

~400 different target proteins

Question 8

How many EF-hand motifs does calmodulin have?

Answer 8

4, two in each of its two lobes.

Question 9

Describe the EF-hand motif.
How many times does this motif occur in the human genome?
How many proteins is this motif found in?

Answer 9

pg 6.
600 times in the genome
250 proteins

Question 10

What does positive cooperativity mean in the context of calmodulin?

Answer 10

It means that when one calcium binds it changes the structure to make it easier for the other three calcium ions to bind.

Question 11

In the coordination sphere of the canonical calcium binding EF-hand loop,

• What are the two most conserved amino acids?
• What are their positions in the EF-hand loop?
• What are their functions?

Answer 11

• Aspartic acid in position 1 gives two oxygen for a bidentate bond with the Ca 2+ ion.
• Glycine in position 6 is the only amino acid small enough to create a shape enough kink in the chain.
  pg 6

Question 12

What calmodulin residues serve to bind inactivated target peptides?

Answer 12

Methionine residues.

Question 13

is the CaM binding domain of Ca 2+ calmodulin dependent protein kinase helical? and what is one amino acid in its binding domain?

Answer 13

• It is NOT helical
• it contains a Tryptophan which serves as an anchor residue for the C-lobe of calmodulin.

Question 14

Calcineurin
Function?
What ions does its A-subunit have?
What activates it?

Answer 14

It is a metallo-phosphatase
Fe 2+ and Zn 2+ ions
Ca 2+ -CaM

Question 15

Recoverin
Function?
How many EF-hand motifs does it have?
How many calcium ions can it bind?

Answer 15

It is a calcium myristoyl switch protein that binds to membranes
It has 4 EF-hand motifs
It can only bind two calcium because the other two sites have mutations in the calcium-liganding amino acids in the calcium binding loops.

Question 16

Describe C2-domains.

Answer 16

They are 130-residues which assist in proteins binding to lipid membranes. They are often calcium dependent and there are about 200 modules found in the human genome. They are largely made of beta-sheets

Question 17

Protein kinase C
Function?
What happens when calcium bound?
What is it activated by?

Answer 17

It phosphorylates serine and threonine residues.
When calcium bound it will head towards and bind to the cell membrane
It is activated by DAG (diacylglycerol) which also activates IP3 which releases Ca 2+ from the ER.

Question 18

How are the signaling molecules DAG and IP3 generated?

Answer 18

pg 8.

Question 19

Do all 10 isozymes of PKC have a C2 domain?
Why does binding to the membrane activate the PKC?

Answer 19

No.
binding to the membrane pulls the pseudosubstrate part of the protein away from the binding site.

Question 20

What do the C1 and C2 domains of PKC bind to?

Answer 20

• C1 binds to DAG (diacyleglycerol)
• C2 binds to phospholipids with phosphatidylserine/ PIP2 headgroups

Question 21

What domain binds first to the lipid membrane in Protein Kinase 3, the C1 or C2 domain?

Answer 21

The C2 domain will bind first to PIP / PtdSer then C1 binding to DAG will follow.

Question 22

What ion does Chlorophyll bind to?

Answer 22

Mg 2+ is bound by the porphyrins chlorophyll a and chlorophyll b

Question 23

How is Mg 2+ often found in the cell?
What coordination geometry does it have?
What ligands does it use in this common form?

Answer 23

Mg 2+ is often bound to ATP (Mg2+-ATP)
It take an octahedral geometry
I uses phosphates and water.