Intracellular calcium-binding proteins: structure and possible functions.

The target proteins for calcium, when it acts as a second messenger, are a group of intracellular, specific calcium-binding proteins that contain EF-hand structures. Calmodulin regulates a number of Ca2+-dependent processes and is present in all eukaryotic cells. Parvalbumin, the S-100 proteins, two vitamin D-dependent Ca2+-binding proteins, and two tumor-associated proteins are present only in a few tissues and are there in distinct cell types serving more specific functions such as Ca2+-buffering or Ca2+-transport. The properties, distribution, and possible roles of these calcium-binding proteins in muscle, brain, and tumor cells are compared.