Calmodulin has two globular domains connected by a single alpha helix (see picture below). Each globular domain contains 2 Ca2+ binding sites. Calmodulin undergoes large conformational changes when bound to Ca2+. Also, when bound to myosin, the globular domains remain relatively unchanged, but the alpha helix connecting them unwound and contains a sharp bend.

Calcium-free Calmodulin:

Calmodulin bound with Calcium:

There is a globular domain located in the
upper-left corner and lower-right corner.
The flexible alpha helix connecting them
runs verticle.

Calmodulin complexed with Rabbit Myosin Light Chain Kinase:

Front view 389x321	Side view 296x333

In the side view, you can see that the two globular domains have come in close
contact with each other. The alpha helix is now unwound and is the u-shape at the
bottom of the picture.

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Last updated: 7/13/01