camstr1

Ca²⁺/Calmodulin

Structure of Ca²⁺/CaM determined by X-ray crystallography. The Ca²⁺-binding loops of the EF-hands are numbered (I-IV), and the amino- (N) and carboxy- (C) termini of the protein, as well as the central linker domain (LD) are indicated in the figure. This structure was reproduced from atomic coordinates deposited in the Brookhaven Protein Data Bank (structure codes 3CLN) using the program Rasmol.

One of the "unusual" features of CaM is the extended, solvent-exposed a-helical linker-domain (LD). This rigid, extended structure is actually an artifact caused by the conditions used to prepare CaM for crystallography. Look at the structure of apo-CaM shown below to get a better picture of how this region of the molecule probably looks in vivo.

For an even better look at this structure, click here to view a model that you can rotate and manipulate. It is based on the same atomic coordinates of vertebrate calmodulin described above.

To view this structure, you will need to have installed Chime or Rasmol, which are both free plug-ins for viewing molecular structures.

Apo-Calmodulin

Structure of apo-calmodulin determined by NMR spectroscopy. The Ca²⁺-binding loops of the EF-hands are numbered (I-IV), and the amino- (N) and carboxy- (C) termini of the protein, as well as the central linker domain (LD) are indicated in the figure. This structure was reproduced from atomic coordinates deposited in the Brookhaven Protein Data Bank (structure code 1CFD) using the program Rasmol.

Notice how much more flexible the central linker domain is in this solution structure. As shown below, this flexibility allows the N- and C-termini of CaM to wrap around and engulf a small region (15-30 amino acids) of a target protein.

For an even better look at this structure, click here to view a model that you can rotate and manipulate based on the NMR structure of apo-calmodulin. As described above, you will need either Rasmol or Chime to view this structure.