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Figure 1
M13(skMLCK) with Ca2+-Calmodulin
Created with RasMac v2.6
M13 peptide from skeletal muscle myosin light chain kinase (skMLCK) was one of the first one to be studied structurally with calmodulin. The structure was solved using the NMR technique by Ikura et al (1992). As predicted by many scientists before the structure was solved, M13 peptide was indeed in an alpha-helix conformation within calmodulin.
In Figure 1, two red residues are the two key bulky hydrophobic residues (Trp4, Phe17) that serve to anchor the peptide to calmodulin. The two bulky residues are separated by 12 residues in the between them. As one can see, the anchor residues fit nicely into the binding pockets.

It was noted from early on that calmodulin has many metionine residues. At first, the role of methionines were not known. The structural study by Ikura et al (1992) revealed that the methionine residues are in the binding pockets. Because the side chains of methionine are very flexible, it was predicted that many different bulky hydrophobic residues can be accomodated in the binding pocket.


Shortly after the NMR study was published, the X-ray crystalography study on the smooth muscle myosin light chain kinase (smMLCK) was completed by Meador et al (1992). Although the method of structural analysis was different, Meador et al showed that the smMLCK also binds to calmodulin with two bulky hydrophobic residues (Trp5, Leu18) serving as anchors. This at first suggested that perhaps all calmodulin-binding peptides possess the same properties. When the structure of CaMKII with calmodulin was published (Meador et al, 1993), 1-14 motif was no longer the sole binding motif for calmodulin-binding peptides. Still, 1-14 motif is the second largest motif in this database.

Figure 2

smMLCK with Ca2+-Calmodulin
Created with RasMac v2.6