Sandbox 213: Difference between revisions
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*'''Ca2+-bound calmodulin''' | *'''Ca2+-bound calmodulin''' | ||
Binding of Ca2+ to the four sites induces a large conformational change causing the terminal helices to expose hydrophobic surfaces and also a long central α-helical segment. Ca2+-bound calmodulin binds to its targets with high affinity (KD ≈10-9 mol.L-1). | Binding of Ca2+ to the four sites induces a large conformational change causing the terminal helices to expose hydrophobic surfaces and also a long central α-helical segment. Ca2+-bound calmodulin binds to its targets with high affinity (KD ≈10-9 mol.L-1). <Structure load='1cll' size='500' frame='true' align='right' caption='Insert caption here' scene='Insert optional scene name here' /> | ||
*'''Calmodulin bound to a target peptide''' | *'''Calmodulin bound to a target peptide''' | ||
To form the bound state, the central residues of the link region unwind form their α-helical arrangement to form a hinge that allows the molecule to bend and wrap itself around the target. The N-terminal and C-terminal regions approach each other and by their hydrophobic surfaces bind to it, rather like two hands holding a rope. This encourages the target sequence to adopt an α-helical arrangement so that it occupies the center of a hydrophobic tunnel. The consequence of this interaction is a conformational change in the target, a state that persists only as long as the Ca2+ concentration remains high. | To form the bound state, the central residues of the link region unwind form their α-helical arrangement to form a hinge that allows the molecule to bend and wrap itself around the target. The N-terminal and C-terminal regions approach each other and by their hydrophobic surfaces bind to it, rather like two hands holding a rope. This encourages the target sequence to adopt an α-helical arrangement so that it occupies the center of a hydrophobic tunnel. The consequence of this interaction is a conformational change in the target, a state that persists only as long as the Ca2+ concentration remains high. | ||
<Structure load='2bbm' size='500' frame='true' align='right' caption='Insert caption here' scene='Insert optional scene name here' /> | |||
When the Ca2+ concentration falls, calcium dissociates and calmodulin is quickly released, inactivating the target. However, at least one important target protein is an exception to this rule. This is CaM-kinase II which can retain its active state after it has been activated by calmodulin. | When the Ca2+ concentration falls, calcium dissociates and calmodulin is quickly released, inactivating the target. However, at least one important target protein is an exception to this rule. This is CaM-kinase II which can retain its active state after it has been activated by calmodulin. | ||