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User:Michael Roberts/BIOL115 CaM: Difference between revisions

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[[Image:1cll.png|left|150px]]
[[Image:CaM.png|left|250px|thumb|Crystal Structure of Calmodulin [[1cll]]]]


<span style="font-size:150%">'''Sequence and structure of EF hands'''</span>
<span style="font-size:150%">'''Sequence and structure of EF hands'''</span>
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<StructureSection load='1cll' size='600' side='right' caption='Structure of human calmodulin (PDB entry [[1cll]])' scene='User:Michael_Roberts/BIOL115_CaM/Wireframe/3'>
<StructureSection load='1cll' size='600' side='right' caption='Structure of human calmodulin (PDB entry [[1cll]])' scene='User:Michael_Roberts/BIOL115_CaM/Wireframe/3'>
'''MOLECULAR MODEL''':
== Molecular Model: ==
We'll start with a simple ball-and-stick representation of the protein. This shows all of the atoms that make up the protein and the bonds between them.
We'll start with a simple ball-and-stick representation of the protein. This shows all of the atoms that make up the protein and the bonds between them.


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The α-helical region is now clearly defined, and there are also regions of β-structure.
The α-helical region is now clearly defined, and there are also regions of β-structure.


Colour key:
''Colour key:''
{{Template:ColorKey_Helix}},
{{Template:ColorKey_Helix}},
{{Template:ColorKey_Strand}}.
{{Template:ColorKey_Strand}}.
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== Calcium Binding ==
'''CALCIUM IONS''':
'''CALCIUM IONS''':
In each EF hand loop, the Ca<sup>2+</sup> ions are bound by amino acid residues in and near the loops.
In each EF hand loop, the Ca<sup>2+</sup> ions are bound by amino acid residues in and near the loops.


The structure shown here has four <scene name='User:Michael_Roberts/BIOL115_CaM/Structure_plus_c/3'>Ca<sup>2+</sup> ions</scene> bound. In this condition, the protein adopts the extended structure shown. The EF hand-forming helices are bent away from the long linking helix, revealing hydrophobic residues and exposing the linking chain.
The structure shown here has four <scene name='User:Michael_Roberts/BIOL115_CaM/Structure_plus_c/3'>calcium ions</scene> bound. In this condition, the protein adopts the extended structure shown. The EF hand-forming helices are bent away from the long linking helix, revealing hydrophobic residues and exposing the linking chain.




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'''INACTIVE CALMODULIN:'''
== Binding to target proteins ==
At resting levels of  cytosolic Ca<sup>2+</sup> (~100 nM), calmodulin exists predominantly in the calcium-free form. This is called apo-calmodulin and <scene name='User:Michael_Roberts/BIOL115_CaM/Inactive_calmodulin/1'>its structure </scene>is more compact.
'''ACTIVE & INACTIVE CALMODULIN:'''
 
At resting levels of  cytosolic Ca<sup>2+</sup> (~100 nM), calmodulin exists predominantly in the calcium-free form. This is called <scene name='User:Michael_Roberts/BIOL115_CaM/Inactive_calmodulin/1'>apo-calmodulin</scene> and its structure is more compact than the structure we saw earlier <scene name='User:Michael_Roberts/BIOL115_CaM/Structure_plus_c/3'>with bound calcium</scene>. Note the extended α-helix linking the two EF-hand-containing domains in the Ca-bound structure, which is interrupted in the <scene name='User:Michael_Roberts/BIOL115_CaM/Inactive_calmodulin/1'>Ca-free form</scene>. Here, the terminal helices are folded down concealing their hydrophobic surfaces and the central chain, which is not now α-helical along its whole length, is not exposed.
The terminal helices are folded down concealing their hydrophobic surfaces and the central chain, which is not a helical along its whole length, is not exposed.




'''CALMODULIN INTERACTS WITH ITS TARGET:'''
'''CALMODULIN INTERACTS WITH ITS TARGET:'''
The Ca2+-bound form of calmodulin with its exposed hydrophobic surfaces that you have already observed can <scene name='User:Michael_Roberts/BIOL115_CaM/Active_calmodulin/1'>interact with a target protein</scene>. It does this by wrapping around a specific sequence on the target molecule, forcing it to adopt an a-helical structure.  
The Ca<sup>2+</sup>-bound form of calmodulin with its exposed hydrophobic surfaces that you have already observed can <scene name='User:Michael_Roberts/BIOL115_CaM/Active_calmodulin/1'>interact with a target protein</scene>. It does this by wrapping around a specific sequence on the target molecule, which is then forced into an α-helical structure.  


The target molecule here (shown in blue) is the calmodulin-regulated enzyme, myosin light chain kinase. Only a short sequence from this protein, the calmodulin binding domain, is shown.
The target molecule here (shown in blue) is the calmodulin-regulated enzyme, myosin light chain kinase. Only a short sequence from this protein, the calmodulin binding domain, is shown.
In this view, <scene name='54/541097/Active_calmodulin/3'>polar and non-polar residues</scene> are coloured in order to highlight the hydrophobic interior of the molecule, which forms the binding site for the myosin light chain kinase calmodulin binding domain.
{{Template:ColorKey_Hydrophobic}},  {{Template:ColorKey_Polar}}
</StructureSection>
</StructureSection>


'''External Resources.'''
'''External Resources.'''
You can view a nice animation of the conformational change undergone by calmodulin upon calcium binding by following this link [http://www.molmovdb.org/cgi-bin/morph.cgi?ID=b097743-28520].
You can view a nice animation of the conformational change undergone by calmodulin upon calcium binding by following this link [http://morph2.molmovdb.org/results.rpy?jobid=8350057535].
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