User:Michael Roberts/BIOL115 CaM
Sequence and structure of EF hands
The EF hand motif is present in a many proteins and it commonly bestows the ability to bind Ca2+ ions. It was first identified in parvalbumin, a muscle protein. Here we will have a look at the Ca2+-binding protein calmodulin, which possesses four EF hands. Calmodulin and its isoform, troponinC, are important intracellular Ca2+-binding proteins.
The structure below, obtained by X-ray crystallography, represents the Ca2+-binding protein calmodulin. It has a dumbell-shaped structure with two identical lobes connected by a central alpha-helix. Each lobe comprises three a helices joined by loops. A helix-loop-helix motif forms the basis of each EF hand.
Click on the 'green links' in the text in the scrollable section below to examine this molecule in more detail.
Let's start with a sinmple of the protein. This shows all the bonds between the atoms that make up the protein. BACKBONE: The wireframe view shows us all the atoms, but this can be too much detail if we're mainly interested ion the overall structure of the protein. This next veiw takes us right doewn to a minimal representation that simply traces the of the protein. The backbone includes the peptide linkages between each amino acid, along with the a-carbon atoms to which R-groups are attached. Notice that helical regions can now be seen. SECONDARY STRUCTURE: This is shown more clearly by a . The computer calculates where regions of secondary structure occur and draws them as ribbons. The a-helical region is now clearly defined, and there are also regions of b-structure. Alpha Helices, Beta Strands , Turns. The short anti-parallel b-sheet between the adjacent EF hand loops are observed in calmodulins from various species. CALCIUM IONS: In each EF hand loop, the Ca2+ ions are bound by residues in and near the loops. The structure shown has four bound. In this condition, the protein adopts the extended structure shown. The EF hand-forming helices are bent away from the long linking helix, revealing hydrophobic residues and exposing the linking chain. CO-ORDINATING RESIDUES: To illustrate how Ca2+ is bound, this display shows the that take part in binding one of the Ca2+ ions. to see this more clearly. End of section |
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