Calmodulin is a small, calcium-binding protein found in all eukaryotic cells. It plays a crucial role in cellular signaling by binding to calcium ions, which causes a change in its shape. This shape change allows calmodulin to interact with various target proteins, influencing numerous cellular processes such as muscle contraction, cell division, and the regulation of enzymes. When calcium levels rise in the cell, calmodulin activates several pathways by binding to specific proteins. This activation can lead to various physiological responses, including changes in metabolism and gene expression. Overall, calmodulin is essential for translating calcium signals into appropriate cellular actions.