Afterhearing the music of Calmodulin,I became interested in exploring the musical properties of other calcium-bindingproteins. The jellyfishat the left was taken from a recent article in Nature describing the tertiarystructure of one of the Aequorins: James F. Head*, Satoshi Inouye,Katsunori Teranish and Osamu Shimomura. The crystal structure ofthe photoprotein aequorin at 2.3 Å resolution. Nature405 (18 May 2000): 372 - 376. For more information on Aequorea, Aequorin and its associated protein GFP, see this article by C.E. Mills.
The 3-Dmodel of Aequorin displayed here is from a different member of theAequorin family. The primary structure of this Aequorin, on which the musicis based, is given in the table below, with Calmodulin for comparison. Aequorin feature markings are from files at SwissProtand PDB. (Errors of interpretation are, of course, mine.) Since my interestwas in the Ca++ binding regions, I have set each binding region on a separateline, even when doing so broke a region of helix. Whereas its sistermolecule Calmodulin has four Ca++ binding sites, Aequorin has only three,having apparently lost one since the genes for the two proteins divergedfrom their common ancestor. Aequorin is also a larger molecule thanCalmodulin.
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Homo sapiens (human)
( ) = alpha helix
Aequorea victoria (jellyfish)
( ) = alpha helix
Notes on the Music:
The music begins with a long introductionin which the theme of the third Ca++-binding domain of the Aequorin sequenceis reiterated several times, in several overlapping voices. The entireAequorin sequence is then introduced on a key change, as the Ca++-bindingtheme gradually fades. Having heard Ca++-binding site 3 several times,you will recognize its appearance in the full Aequorin sequence. After the full sequence is repeated, it returns, this time with the alpha,beta and turn regions sounding in different voices: the alpha helixregions are clearly marked by a parallel voice set a fourth above the mainmelodic line played by marimba, and the turns by wood blocks. Afterthis second reiteration of the full aequorin sequence, the sister proteinCalmodulin drops in for a brief appearance. Aequorin then returnswith fragments of the Ca++-binding theme to finish the piece.