The Molecular History of Eukaryotic Life  Calcium/ Calmodulin 


David Nelson  Dec. 13, 2000

	Calmodulin is a calcium binding protein that activates many different enzymes 
such as plasma membrane calcium pumps, phosphodiesterases, kinases(CAM kinase II) and 
phosphatases (calcineurin).  It binds calcium at low micromolar concentrations, changes 
its conformation and binds to its target enzymes.  Calmodulin is found in every eukaryote 
ever looked at, but it is not found in bacteria.  A report has been published that a 
calmodulin like protein is present in Halobacterium salinarium an archeabacterium.  This 
protein binds calcium, it activated cAMP phosphodiesterase and is inhibited by calmodulin 
inhibitors, but the sequence is not known yet.  

	The structure of calmodulin has four EF hands that are motifs that bind calcium.  
The EF hands are numbered I, II III and IV.  I and III are more similar to each other 
than they are to II and IV.  II and IV are more similar to each other than they are to I 
and III.  The interpretation of this is that the protein evolved from a gene with a 
single calcium binding motif that duplicated and diverged for a time then duplicated 
again.  The original one domain gene is now vanished into the distant past and may not 
exist any more, or it will probably be impossible to detect the similarity to it.  It is 
unfortunate that many evolutionary questions of origins cannot be solved because the 
process of evolution has erased the books.

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