User:Alice Harmon/EF Hand
EF-hands are calcium-binding motifs found in hundreds of proteins. They bind calcium ions with high affinity (Kds are in the micromolar range) and selectivity, and this property allows EF-hand proteins to sense changes in intracellular calcium. In unstimulated cells cellular free calcium concentrations [Ca2+]c are in the nanomolar range (~10 nM in animal cells and ~200 nM in plant cells), and EF-hands are generally unoccupied by Ca2+. Upon stimulation, Ca2+ enters the cytosol from either outside the cell or from internal organelles, and [Ca2+]c rises to the micromolar range. EF-hands bind Ca2+, and this binding causes a conformational change that alters the activity of the protein.
The name EF-hand originated from the first such structure to be described, which was in the protein parvalbumin. In this protein calcium is bound by a helix-loop-helix structure that is formed by the E and F helices (letters assigned to helices in the order that they occur starting at the N-terminus). See the annotated protein sequence for carp parvalbumin here [1].
Below are EF-hands found in parvalbumin, calmodulin, and calcium-dependent protein kinase.
4cpv |
1prw |
3HX4 |