page_title: Calmodulin
hierarchical_section_title: Calmodulin
caption_attribution_description: English: The helix-loop-helix EF-hand Ca2+ binding motif. (left) Cartoon illustration of the canonical EF-hand Ca2+-binding motif. The EF-hand motif contains a 29-residue helix-loop-helix topology, much like the spread thumb and forefinger of the human hand. Ca2+ is coordinated by ligands within the 12-residue loop, including seven oxygen atoms from the sidechain carboxyl or hydroxyl groups (loop sequence positions 1, 3, 5, 12), a main chain carbonyl group (position 7), and a bridged water (via position 9). Residue at position 12 serves as a bidentate ligand. (middle) The Ca2+ binding pocket adopts a pentagonal bipyramidal geometry. n stands for hydrophobic residue. (right) 3D structure of a typical canonical EF-hand motif from calmodulin (PDB code: 3cln). Ca3D structure of a typical canonical EF-hand motif from calmodulin (PDB code: 3cln). Ca3D structure of a typical canonical EF-hand motif from calmodulin (PDB code: 3cln). Calcium is chelated by ligands from a 12-residue loop.
context_page_description: Calmodulin is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca²⁺, and the binding of Ca²⁺ is required for the activation of calmodulin. Once bound to Ca²⁺, calmodulin acts as part of a calcium signal transduction pathway by modifying its interactions with various target proteins such as kinases or phosphatases.
context_section_description: Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca²⁺, and the binding of Ca²⁺ is required for the activation of calmodulin. Once bound to Ca²⁺, calmodulin acts as part of a calcium signal transduction pathway by modifying its interactions with various target proteins such as kinases or phosphatases.
caption: The helix–loop–helix structure of the calcium-binding EF hand motif
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