I am interested in the calmodulin interactions with its target peptides. One synthetic target peptide is M13, which is the basis for many GECIs such as GCaMP. My question is, in the calcium-unbound state, is it the case that Calmodulin binds M13, but just in a different conformation than in the calcium bound state, or does calmodulin not bind M13 at all until there is calcium?
In a similar vein, does anyone know of a CaM target that is completely unbound in the absence of calcium (apo-CaM) but bound with calcium (holo-CaM)?
Actually all the latest GCaMPs are based on RS20 and not M13. It's funny how nearly all papers are mislabeling it.
As far as I know all the standard peptides used for CaM-peptide interaction are normally not bound to CaM in the absence of Ca2+. (But in the biology, things are never 1 or 0).
People already used it as a Calcium integrator for mapping neural activity in Drosophila, e.g. here, implying the the SN-ratio between plusminus Ca2+ must be pretty good (good enough at least as a transcriptional reporter).
http://www.nature.com/neuro/journal/v18/n6/pdf/nn.4016.pdf
Article A Transcriptional Reporter of Intracellular Ca in Drosophila
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