Calcium-free Calmodulin: Difference between revisions
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The structure of calcium-free calmodulin was discovered by doing several different NMR experiments that included ROE, reverse labelling of Phe residues, and 3-bond J-couplings. <ref name="4CRT"/> It was theorized that by comparing the results of the NMR experiments for the apo calmodulin with the calcium-bound calmodulin, information could be gleaned as to the structural changes that occur when calcium is bound. It was discovered that the series of residues from Met76 to Ser81 which comprised the flexible link between the N-terminal domain and the C-terminal domain were in a helical form in apo calmodulin, but not in calcium-bound calmodulin. <ref name="4CRT"/> These findings suggested that when calcium binds to both domains on calmodulin, a conformational change occurs that involves the unwinding of this helical arrangement. <ref name="4CRT"/> It was further inferred that when calcium binds to calmodulin, the resulting conformational change creates hydrophobic pockets on the surface of the N and C domains which were not present in the apo state. <ref name="4CRT"/><ref name="7CRT">Ikura, M et al. Solution structure of a calmodulin-target peptide complex by mulit-dimensional NMR. Science, 256:632-638</ref> There are proteins with similar structures to calmodulin, and troponin was in fact used as a comparison model, as it was highly homologous (51% sequence identity)to calmodulin. <ref name="4CRT"/> | The structure of calcium-free calmodulin was discovered by doing several different NMR experiments that included ROE, reverse labelling of Phe residues, and 3-bond J-couplings. <ref name="4CRT"/> It was theorized that by comparing the results of the NMR experiments for the apo calmodulin with the calcium-bound calmodulin, information could be gleaned as to the structural changes that occur when calcium is bound. It was discovered that the series of residues from Met76 to Ser81 which comprised the flexible link between the N-terminal domain and the C-terminal domain were in a helical form in apo calmodulin, but not in calcium-bound calmodulin. <ref name="4CRT"/> This conclusion was supported by experiments with proteases that digested this region in the calcium-bound state, but not the apo state, meaning that this region is protected in the apo state. <ref name="4CRT">Angela M. Gronenborn and G. Marius Clore. Identification of N-terminal helix capping boxes by means of 13C chemical shifts. Journal of Biomolecular NMR, 4:1994</ref> These findings suggested that when calcium binds to both domains on calmodulin, a conformational change occurs that involves the unwinding of this helical arrangement. <ref name="4CRT"/> It was further inferred that when calcium binds to calmodulin, the resulting conformational change creates hydrophobic pockets on the surface of the N and C domains which were not present in the apo state. <ref name="4CRT"/><ref name="7CRT">Ikura, M et al. Solution structure of a calmodulin-target peptide complex by mulit-dimensional NMR. Science, 256:632-638</ref> There are proteins with similar structures to calmodulin, and troponin was in fact used as a comparison model, as it was highly homologous (51% sequence identity)to calmodulin. <ref name="4CRT"/> | ||
