Sandbox 213: Difference between revisions
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The affinity of the individual Ca2+ ion binding sites are in the range 10-5-10-6 mol.L-1 and adjacent sites bind Ca2+ with positive cooperativity, so that attachment of the first Ca2+ ion enhances the affinity of its neighbour. This has the effect of making the protein sensitive to small changes in the concentration of Ca2+ within the signaling range. Ca2+-calmodulin itself has no intrinsic catalytic activity. Its action depends on its close association with a target enzyme. | The affinity of the individual Ca2+ ion binding sites are in the range 10-5-10-6 mol.L-1 and adjacent sites bind Ca2+ with positive cooperativity, so that attachment of the first Ca2+ ion enhances the affinity of its neighbour. This has the effect of making the protein sensitive to small changes in the concentration of Ca2+ within the signaling range. Ca2+-calmodulin itself has no intrinsic catalytic activity. Its action depends on its close association with a target enzyme. | ||
''' | *'''Three-dimensional structure of apocalmodulin''' | ||
In the absence of bound Ca2+, the helices of calmodulin pack so that their hydrophobic side chains are not exposed. In this form it is unable to interact with its targets5. | In the absence of bound Ca2+, the helices of calmodulin pack so that their hydrophobic side chains are not exposed. In this form it is unable to interact with its targets5. | ||
(IMAGE CALMODULINE SEULE) | (IMAGE CALMODULINE SEULE) | ||
''' | *'''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) 5. | 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) 5. | ||
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''' | *'''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 high5. | 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 high5. | ||