2. PDB ID 2VN9

3. Calmodulin  CALcium MODUlated proteIN (CaM)  Found in Eukarya and Bacteria  Consists of 148 amino acids  Abundant in cytoplasm  Role: senses calcium levels and relays signals to various calcium sensitive enzymes, ion channels and other proteins.  Structure of calmodulin  CaM has a bilobal structure and each domain is connected by a central linker region.  Central linker region forms alpha helix  CaM has two active sites and are remarkably rich in methionine residues. 1,2 Pdb id: 2L7L. Yellow color: central linker region Red: alpha helices forming the secondary structure Blue: calcium ions bound to calmodulin.

4. CaM has pI value of 4.3 which corresponds to the presence of Aspartates and glutamates, and it is been confirmed by the studies that these are the amino acids that are responsible for the binding of calcium ions as they have negative charge and attracts positively charged ions. 1,2

5. Grey color: alpha helices Red: central linker region.

6. Grey- alpha helices Blue-calcium ions bound to the active sites. And the ball and stick model of aspartates and glutamates which binds to the calcium ion.

8. Alpha helices with hydrophobic methionine residues which binds to the target protein.

9. FUNCTION OF CALMODULIN:  Regulate many cellular functions such as inflammation, metabolism, muscle contraction, nerve growth and immune response.  Calmodulin binds and activates kinases and phosphatases that play significant roles in cell signaling, ion transport and cell death.  Calcium-bound calmodulin forms a critical subunit for the regulatory enzyme phosphorylase kinase, which in turn is a regulator for glycogen breakdown.

11. References: 1.Tao Yuan, Hans, J. Vogel. (1999) Substitution of the methionine residues of Calmodulin with the unnatural amino acid analogs ethionine and norleucine: Biochemical and spectroscopic studies. Protein Science. 8: 113-121. 2.Mika Aoyagi, Andrew, S., Arvaii, John A. Trainer., and Elizabeth, D.Getzoff (2003) Structural basis for endothelial nitric oxide synthase binding to Calmodulin. EMBO J. Feb 17, 766-775.