Calmodulin (CaM) – calcium modulated protein – regulates various protein targets. It is used by various proteins as calcium sensor and signal transducer by binding to their calcium binding domain (CBD). It undergoes conformational change upon binding Ca++ via its 4 EF hand motives and can undergo post-translational modification. More details on apo-CaM in Calcium-free Calmodulin.
Maximum Occurrence, a method for making rigorous numerical assessments about the maximum percent of time that a conformer of a flexible macromolecule can exist and still be compatible with the experimental data, was used to probe the conformational disorder of Calmodulin[1].
Figure 3: Orientation tensor representation for 400 conformational states of Calmodulin, color coded according to their MO values (from less than 5% in blue to more than 30% in red).To better explain their meaning, 10 randomly chosen models are shown as cartoons and then replaced by the three axes of their color-coded orientation tensors.
It was shown that the open (1cll) and closed (1prw) conformers can have MO of only 15% and 5% respectively.
Calmodulin in Motion
The clip represents Calmodulin in motion. At the beginning it is shown moving in the unbound form (ApoCaM), and it changes its conformation when Calcium ions are present in the medium (CaCaM).
<swf width="720" height="576">/flash/Apo_CaM_CaCaM.swf</swf>
Motion of ApoCaM is elaborated on the basis of 23 conformations derived from NMR file 1cfc, using the 3D animation program Blender, and according to a system to be published soon (Zini et al., manuscript in preparation). The transition from ApoCaM to CaCaM is elaborated with Blender starting with conformation 21 of 1cfc to arrive in conformation 11 of pdb file 1x02.
Surface rendering is also elaborated using Blender, and shows the lipophilic potential as a scale of white-black and smooth-rough, form the most lipophilic to the hydrophilic. Electrostatic potential is represented as a series of lines moving in the direction Positive to Negative, elaborated according to a scheme to be published soon (Andrei et al., in preparation). As most lines are moving towards Calmodulin, one can learn that the protein is slightly acidic (negative partial charges on its surface).
This movie was created by Andrei, Zini et al., of the
Scientific Visualization Unit,
Institute of Clinical Physiology - CNR of Itlay.
Conformational change of Calmodulin
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