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Figure 1
Peptide from CaMKII and Ca2+-Calmodulin
Created with RasMac v2.6
The X-ray crystal structure of the peptide from the alpha subunit of Calmodulin-dependent kinase II and calmodulin was solved by Meader et al in 1993. The structure is somewhat superficially similar to those of skMLCK or smMLCK and Ca2+-Calmodulin. Two bulky hydrophobic residues contact methionine residues in the binding pocket of calmodulin. The overall conformation of the complex is globular. Peptide itself forms an alpha helix. In Figure 1, the two hydrophobic residues are coloured red in the picture to the left. They are Leu10 and Leu19.
However, having two hydrophobic anchor residues are where the similarities to the smMLCK and skMLCK peptides end. First of all, the spacing between the anchoring residues are down from 12 to 8. Second, the glutamate residues of Ca2+-calmodulin participates more so than in the smMLCK or skMLCK. Many side chains in the calmodulin show different conformation from the smMLCK or skMLCK story. In addition, the linker region between the two domains show more flexibility than previously thought by unravelling the alpha-helix further.
Here, we begin to see why calmodulin is able to bind so many peptides without apparent sequence homology. First, methionine residues in the binding pocket provide the variety in the anchoring residues. Second, the linker region is able to change its conformation to accomodate many different peptides of different lengths. Third, calmodulin changes its conformation drastically upon binding calcium ions. In combination, it is no wonder there are so many different peptides that bind calmodulin without apparent sequence homology.