page_title: Calmodulin
section_title: Role in smooth muscle contraction
hierarchical_section_title: Calmodulin / Role in animals / Specific examples / Role in smooth muscle contraction
caption_attribution_description: English: This is an image of Calmodulin (with 4 Calcium ions bound) binding to myosin light chain (MLC) kinase
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 plays an important role in excitation contraction (EC) coupling and the initiation of the cross-bridge cycling in smooth muscle, ultimately causing smooth muscle contraction. In order to activate contraction of smooth muscle, the head of the myosin light chain must be phosphorylated. This phosphorylation is done by myosin light chain (MLC) kinase. This MLC kinase is activated by a calmodulin when it is bound by calcium, thus making smooth muscle contraction dependent on the presence of calcium, through the binding of calmodulin and activation of MLC kinase.
  Another way that calmodulin affects muscle contraction is by controlling the movement of Ca²⁺ across both the cell and sarcoplasmic reticulum membranes. The Ca²⁺ channels, such as the ryanodine receptor of the sarcoplasmic reticulum, can be inhibited by calmodulin bound to calcium, thus affecting the overall levels of calcium in the cell. Calcium pumps take calcium out of the cytoplasm or store it in the endoplasmic reticulum and this control helps regulate many downstream processes.
  This is a very important function of calmodulin because it indirectly plays a role in every physiological process that is affected by smooth muscle contraction such as digestion and contraction of arteries (which helps distribute blood and regulate blood pressure).
caption: Calmodulin bound to a peptide from MLC kinase (PDB: 2LV6​)
exif: {"Image ExifOffset": "28", "EXIF ImageDescription": "ImageSource=RCSB PDB; StructureID=2lv6; DOI=http://dx.doi.org/10.2210/pdb2lv6/pdb;"}