The many structural faces of calmodulin: a multitasking molecular jackknife
Calmodulin (CaM) is a highly conserved protein and a crucial calcium sensor in eukaryotes. CaM is a regulator of hundreds of diverse target proteins. A wealth of studies has been carried out on the structure of CaM, both in the unliganded form and in complexes with target proteins and peptides. The outcome of these studies points toward a high propensity to attain various conformational states, depending on the binding partner. The purpose of this review is to provide examples of different conformations of CaM trapped in the crystal state. In addition, comparisons are made to corresponding studies in solution. The different CaM conformations in crystal structures are also compared based on the positions of the metal ions bound to their EF hands, in terms of distances, angles, and pseudo-torsion angles. Possible caveats and artifacts in CaM crystal structures are discussed, as well as the possibilities of trapping biologically relevant CaM conformations in the crystal state.
KeywordsProtein conformation Crystal structure Complex Calcium X-Ray crystallography Calmodulin
Death-associated protein kinase
Protein Data Bank
This work has been supported by grants from the Academy of Finland, the Sigrid Juselius Foundation, and the Hamburg Foundation for Science and Research.
Conflict of interest
The author declares that he has no conflict of interest.
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