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<Structure load='3CLN' size='300' frame='true' align='left' caption='Calcium-bound calmodulin' scene='Insert optional scene name here' /> | <Structure load='3CLN' size='300' frame='true' align='left' caption='Calcium-bound calmodulin' scene='Insert optional scene name here' /> | ||
[[Calmodulin]] (CaM) for Calcium-Modulated protein is an important protein that intervenes in a wide range of activities. | [[Calmodulin]] (CaM) for Calcium-Modulated protein is an important protein that intervenes in a wide range of activities<ref name="Najl V Valeyev1, Declan G Bates1, Pat Heslop-Harrison1,2, Ian Postlethwaite1 and Nikolay V Kotov. Elucidating the mechanisms of cooperative calcium-calmodulin interactions: a structural systems biology approach.BMC Systems Biology 2008, 2:48 doi:[[10.1186/1752-0509-2-48]]"/>. | ||
CaM is expressed in many cell types and can have different subcellular locations, including the cytoplasm, within organelles, or associated with the plasma or organelle membranes. | CaM is expressed in many cell types and can have different subcellular locations, including the cytoplasm, within organelles, or associated with the plasma or organelle membranes. | ||
Indeed, it is a small (16.7 kDa = 148 aa) and highly conserved protein that is necessary in all eukaryotic cells because it represents an essential calcium sensor with troponin C its isoform. | Indeed, it is a small (16.7 kDa = 148 aa) and highly conserved protein that is necessary in all eukaryotic cells because it represents an essential calcium sensor with troponin C its isoform. | ||
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'''Calmodulin''' [http://www.rcsb.org/pdb/101/motm_disscussed_entry.do?id=3cln] | '''Calmodulin''' [http://www.rcsb.org/pdb/101/motm_disscussed_entry.do?id=3cln] | ||
[[Image:calmodulin_Ca_site.gif|right|200px]] | |||
Calmodulin contains four Ca<sup>2+</sup> binding sites and the binding of calcium induces a conformational change in calmodulin that can cause the activation of key enzymes such as kinases or phosphatases proteins (especially phosphorylase kinases) which are not necessarily themselves Ca<sup>2+</sup>-sensitive and allows a large diversity of cellular response. | Calmodulin contains four Ca<sup>2+</sup> binding sites and the binding of calcium induces a conformational change in calmodulin that can cause the activation of key enzymes such as kinases or phosphatases proteins (especially phosphorylase kinases) which are not necessarily themselves Ca<sup>2+</sup>-sensitive and allows a large diversity of cellular response. | ||
The calmodulin structure has been determined by NMR. This method reveals that calmodulin is a long molecule which looks like a '''dumbbell''' because it contains '''two globular domains''' (the <scene name='Sandbox_213/N-lobe/1'>N-lobe</scene> and the <scene name='Sandbox_213/C-lobe/1'>C-lobe</scene>) linked by a <scene name='Sandbox_213/flexible α-helix/1'>flexible α-helix</scene>. | The calmodulin structure has been determined by NMR. This method reveals that calmodulin is a long molecule which looks like a '''dumbbell''' because it contains '''two globular domains''' (the <scene name='Sandbox_213/N-lobe/1'>N-lobe</scene> and the <scene name='Sandbox_213/C-lobe/1'>C-lobe</scene>) linked by a <scene name='Sandbox_213/flexible α-helix/1'>flexible α-helix</scene> <ref name="Najl V Valeyev1, Declan G Bates1, Pat Heslop-Harrison1,2, Ian Postlethwaite1 and Nikolay V Kotov. Elucidating the mechanisms of cooperative calcium-calmodulin interactions: a structural systems biology approach.BMC Systems Biology 2008, 2:48 doi:[[10.1186/1752-0509-2-48]]"/>. | ||
Each lobe contains a pair of <scene name='Sandbox_213/helix-loop-helix/1'>helix-loop-helix</scene> motifs (called EF-hand or calmodulin-fold) that can bind two Ca<sup>2+</sup> ions. However those lobes do not have the same properties because the C-lobe has higher Ca<sup>2+</sup> affinity than the N-lobe. | Each lobe contains a pair of <scene name='Sandbox_213/helix-loop-helix/1'>helix-loop-helix</scene> motifs (called EF-hand or calmodulin-fold) that can bind two Ca<sup>2+</sup> ions. However those lobes do not have the same properties because the C-lobe has higher Ca<sup>2+</sup> affinity than the N-lobe. | ||
The two EF-hands are located in the vicinity of each other. Those neighboring sited are very likely to structurally influence each other upon Ca<sup>2+</sup> binding to one of them. | The two EF-hands are located in the vicinity of each other. Those neighboring sited are very likely to structurally influence each other upon Ca<sup>2+</sup> binding to one of them. | ||
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The affinity of the individual Ca<sup>2+</sup> ion binding sites are in the range 10<sup>−5</sup>-10<sup>−6</sup> mol.L<sup>−1</sup> and adjacent sites bind Ca<sup>2+</sup> with positive cooperativity, so that attachment of the first Ca<sup>2+</sup> ion enhances the affinity of its neighbour. This has the effect of making the protein sensitive to small changes in the concentration of Ca<sup>2+</sup> within the signaling range. | The affinity of the individual Ca<sup>2+</sup> ion binding sites are in the range 10<sup>−5</sup>-10<sup>−6</sup> mol.L<sup>−1</sup> and adjacent sites bind Ca<sup>2+</sup> with positive cooperativity, so that attachment of the first Ca<sup>2+</sup> ion enhances the affinity of its neighbour. This has the effect of making the protein sensitive to small changes in the concentration of Ca<sup>2+</sup> within the signaling range. | ||
Ca<sup>2+</sup>-calmodulin itself has no intrinsic catalytic activity. Its action depends on its close association with a target enzyme. The C-terminal domain solution structure is similar while the EF hands of the N-terminal domain are considerably less open. The backbone flexibility within calmodulin is key to its ability to bind a wide range of targets. | Ca<sup>2+</sup>-calmodulin itself has no intrinsic catalytic activity. Its action depends on its close association with a target enzyme. The C-terminal domain solution structure is similar while the EF hands of the N-terminal domain are considerably less open. The backbone flexibility within calmodulin is key to its ability to bind a wide range of targets <ref name="Halling DB, Georgiou DK, Black DJ, Yang G, Fallon JL, Quiocho FA, Pedersen SE, Hamilton SL. Determinants in CaV1 channels that regulate the Ca2+ sensitivity of bound calmodulin. J Biol Chem. 2009 Jul 24;284(30):20041-51. Epub 2009 May 27. PMID:19473981 doi:[[10.1074/jbc.M109.013326]]"/>. | ||
Up to four calcium ions are bound by calmodulin via its four EF hand motifs. EF hands supply an electronegative environment for ion coordination. After calcium binding, hydrophobic methyl groups from methionine residues become exposed on the protein via conformational change. | Up to four calcium ions are bound by calmodulin via its four EF hand motifs. EF hands supply an electronegative environment for ion coordination. After calcium binding, hydrophobic methyl groups from methionine residues become exposed on the protein via conformational change. | ||
This presents hydrophobic surfaces, which can in turn bind to Basic Amphiphilic Helices (BAA helices) on the target protein. These helices contain complementary hydrophobic regions. The flexibility of Calmodulin's hinged region allows the molecule to "wrap around" its target. This property allows it to tightly bind to a wide range of different target proteins.</StructureSection> | This presents hydrophobic surfaces, which can in turn bind to Basic Amphiphilic Helices (BAA helices) on the target protein. These helices contain complementary hydrophobic regions. The flexibility of Calmodulin's hinged region allows the molecule to "wrap around" its target. This property allows it to tightly bind to a wide range of different target proteins. <ref name="Houdusse A, Gaucher JF, Krementsova E, Mui S, Trybus KM, Cohen C. Crystal structure of apo-calmodulin bound to the first two IQ motifs of myosin V reveals essential recognition features. Proc Natl Acad Sci U S A. 2006 Dec 19;103(51):19326-31. Epub 2006 Dec 6. PMID :[[17151196]]"/>. </StructureSection> | ||
*'''Three-dimensional structure of apocalmodulin''' | *'''Three-dimensional structure of apocalmodulin''' | ||
[[Image:Apocalmodulin.png|right|100px]] | [[Image:Apocalmodulin.png|right|100px]] | ||
In the absence of bound Ca<sup>2+</sup>, the helices of calmodulin pack so that their hydrophobic side chains are not exposed. In this form it is unable to interact with its targets.The C-terminal lobe of each CaM adopts a semi-open conformation that grips the first part of the IQ motif (IQxxxR), whereas the N-terminal lobe adopts a closed conformation that interacts more weakly with the second part of the motif (GxxxR). <ref name="Houdusse A, Gaucher JF, Krementsova E, Mui S, Trybus KM, Cohen C. Crystal structure of apo-calmodulin bound to the first two IQ motifs of myosin V reveals essential recognition features. Proc Natl Acad Sci U S A. 2006 Dec 19;103(51):19326-31. Epub 2006 Dec 6. PMID:[[17151196]]"/>. | In the absence of bound Ca<sup>2+</sup>, the helices of calmodulin pack so that their hydrophobic side chains are not exposed. In this form it is unable to interact with its targets.The C-terminal lobe of each CaM adopts a semi-open conformation that grips the first part of the IQ motif (IQxxxR), whereas the N-terminal lobe adopts a closed conformation that interacts more weakly with the second part of the motif (GxxxR). <ref name="Houdusse A, Gaucher JF, Krementsova E, Mui S, Trybus KM, Cohen C. Crystal structure of apo-calmodulin bound to the first two IQ motifs of myosin V reveals essential recognition features. Proc Natl Acad Sci U S A. 2006 Dec 19;103(51):19326-31. Epub 2006 Dec 6. PMID:[[17151196]]"/>. | ||
[[Image:Calmodulin bound to calcium.png|right|100px]] | [[Image:Calmodulin bound to calcium.png|right|100px]] | ||
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Calmodulin uses a linear sequence of 12 amino acids to bind Ca<sup>2+</sup>. | Calmodulin uses a linear sequence of 12 amino acids to bind Ca<sup>2+</sup>. | ||
Binding of Ca<sup>2+</sup> 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. Ca<sup>2+</sup>-bound calmodulin binds to its targets with high affinity (K<sub>D</sub>≈10<sup>−9</sup> mol.L<sup>−1</sup>). | Binding of Ca<sup>2+</sup> 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. Ca<sup>2+</sup>-bound calmodulin binds to its targets with high affinity (K<sub>D</sub>≈10<sup>−9</sup> mol.L<sup>−1</sup>)<ref name="Fallon JL, Quiocho FA. A closed compact structure of native Ca(2+)-calmodulin. Structure. 2003 Oct;11(10):1303-7. PMID :[[14527397]]"/>. | ||
*'''Calmodulin bound to a target peptide''' | *'''Calmodulin bound to a target peptide''' | ||
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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. | 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. | 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 Ca<sup>2+</sup> concentration remains high. | The consequence of this interaction is a conformational change in the target, a state that persists only as long as the Ca<sup>2+</sup> concentration remains high <ref name="Fallon JL, Quiocho FA. A closed compact structure of native Ca(2+)-calmodulin. Structure. 2003 Oct;11(10):1303-7. PMID :[[14527397]]"/>. | ||
When the Ca<sup>2+</sup> 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 Ca<sup>2+</sup> 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. | ||
=CaMII kinase= | =CaMII kinase= | ||
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Calmodulin plays an important role through kinase enzymes such as calcium/calmodulin-dependent kinase II (CaMKII) that is a multifunctional serine/threonine kinase found in many tissues. Activation of CaMKII contributes to synaptic plasticity and regulation of excitory synaptic transmission. The regulatory domain of CaMKII contains an autophosphorylation site, which is essential for its calcium-dependent activation. | Calmodulin plays an important role through kinase enzymes such as calcium/calmodulin-dependent kinase II (CaMKII) that is a multifunctional serine/threonine kinase found in many tissues. Activation of CaMKII contributes to synaptic plasticity and regulation of excitory synaptic transmission. The regulatory domain of CaMKII contains an autophosphorylation site, which is essential for its calcium-dependent activation <ref name="Evans TI, Shea MA. Energetics of calmodulin domain interactions with the calmodulin binding domain of CaMKII. Proteins. 2009 Jul;76(1):47-61. PMID:19089983. doi :[[10.1002/prot.22317]]"/>. | ||
CaM kinases have a catalytic N-terminal domain, a regulator domain and | CaM kinases have a catalytic N-terminal domain, a regulator domain and a domain of association. Many CaM form an holoenzyme with a dodecameric structure(the catalytics domains are found one's way out side) that permit to phosphorylate the residues between the sub-unit. Without Ca2+/calmodulin, the catalytic domain is self-inhibited by the regulator domain, which contains one sequence of type pseudo-substrate. Many CaM kinases give an homo-oligomeres or hetero-oligomeres. When there is an activation by the Ca2+/calmodulin complex, the actif CaM kinases are autophosphorylated one by one at the level of the threonine 286 residues. | ||
=Family members= | =Family members= | ||
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<ref group="xtra">doi:10.1186/1752-0509-2-48</ref><references group="xtra"/> | <ref group="xtra">doi:10.1186/1752-0509-2-48</ref><references group="xtra"/> | ||
<ref group="xtra"> doi: 10.1074/jbc.M109.013326</ref><references group="xtra"/> | |||
<ref group="xtra">PMID:17151196</ref><references group="xtra"/> | |||
<ref group="xtra">PMID:15194112</ref><references group="xtra"/> | |||
<ref group="xtra">PMID:14527397</ref><references group="xtra"/> | <ref group="xtra">PMID:14527397</ref><references group="xtra"/> | ||
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<ref group="xtra">doi:10.1002/prot.22317</ref><references group="xtra"/> | <ref group="xtra">doi:10.1002/prot.22317</ref><references group="xtra"/> | ||
=Proteopedia page contributors and editor= | =Proteopedia page contributors and editor= | ||
Tonazzini Saphia, Planchenault Charlène | Tonazzini Saphia, Planchenault Charlène | ||