M. R. Nelson

Structures of EF-hand Ca 2+-binding proteins: Diversity in the organization, packing and response to Ca 2+ Binding

The growing database of three-dimensional structures of EF-hand calcium-binding proteins is revealing a previously unrecognized variability in the coformations and organizations of EF-hand binding motifs. The structures of twelve different EF-hand proteins for which coordinates are publicly available are discussed and related to their respective biological and biophysical properties. The classical picture of calcium sensors and calcium signal modulators is presented, along with variants on the basic theme and new structural paradigms.© Kluwer Academic Publishers

The EF-hand domain: a globally cooperative structural unit.

EF‐hand Ca2+‐binding proteins participate in both modulation of Ca2+ signals and direct transduction of the ionic signal into downstream biochemical events. The range of biochemical functions of these proteins is correlated with differences in the way in which they respond to the binding of Ca2+. The EF‐hand domains of calbindin D9k and calmodulin are homologous, yet they respond to the binding of calcium ions in a drastically different manner. A series of comparative analyses of their structures enabled the development of hypotheses about which residues in these proteins control the calcium‐induced changes in conformation. To test our understanding of the relationship between protein sequence and structure, we specifically designed the F36G mutation of the EF‐hand protein calbindin D9k to alter the packing of helices I and II in the apoprotein. The three‐dimensional structure of apo F36G was determined in solution by nuclear magnetic resonance spectroscopy and showed that the design was successful. Surprisingly, significant structural perturbations also were found to extend far from the site of mutation. The observation of such long‐range effects provides clear evidence that four‐helix EF‐hand domains should be treated as a single globally cooperative unit. A hypothetical mechanism for how the long‐range effects are transmitted is described. Our results support the concept of energetic and structural coupling of the key residues that are crucial for a proteins fold and function.