Molecule of the Month: Calmodulin
Calcium ions rapidly deliver signals to control processes such as muscle contraction, nerve signaling, and fertilization
Structures and Signals
A Functionally Versatile Molecule
Flexibility of Calmodulin
Exploring the Structure
Calmodulin in Action
Calmodulin changes shape when it binds to calcium and can activate over 300 essential proteins. Each of its four high-affinity calcium binding sites, called EF-hands, contains a characteristic loop flanked by two alpha helices. The bottom image illustrates calcium ion coordination in the fourth EF-hand, where the positively-charged calcium ion forms seven bonds with negatively-charged oxygen atoms from three aspartates, one glutamate, one backbone carbonyl, and one water molecule. After all four calcium ions bind, calmodulin shifts from a closed shape (PDB entry 1cfd, left) to an open shape (PDB entry 1cll, middle). Its newly-exposed central alpha helix (pink) can wrap around target proteins like myosin light chain kinase (PDB entry 2bbm, right), facilitating interaction between hydrophobic amino acids on the protein surface, including numerous methionines (shown in bright orange).
Select the JSmol tab to explore these structures in an interactive view.
This JSmol was designed and illustrated by Xinyi Christine Zhang.
August 2003, Shuchismita Dutta, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2003_8