Calcium-dependent proteins are proteins that require the presence of calcium ions (Ca²⁺) to function properly. These proteins play crucial roles in various biological processes, including muscle contraction, neurotransmitter release, and cell signaling. When calcium binds to these proteins, it induces a conformational change that activates or enhances their activity. One well-known group of calcium-dependent proteins is the calmodulin family, which regulates numerous enzymes and cellular functions. Other examples include troponin, involved in muscle contraction, and synaptotagmin, which plays a role in neurotransmitter release at synapses. These proteins are essential for maintaining cellular homeostasis and facilitating communication within and between cells.