Calmodulin is a small, calcium-binding protein found in all eukaryotic cells. It plays a crucial role in cellular signaling by changing its shape when it binds to calcium ions. 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 proteins like calcium/calmodulin-dependent protein kinases (CaMKs). These interactions help transmit signals that regulate important functions, making calmodulin essential for maintaining cellular health and responding to environmental changes.