calciumdependent

Calcium-dependent describes processes, proteins, or enzymes whose activity or function relies on calcium ions (Ca2+). In cells, calcium acts as a versatile second messenger; transient changes in intracellular Ca2+ concentration translate extracellular signals into a wide array of biological responses.

The mechanism typically involves calcium binding to specific motifs on target proteins, most commonly EF-hand motifs. Ca2+ binding induces conformational changes that enable interaction with substrates, activation of enzymes, or modulation of ion channels. Some proteins act as calcium sensors that recruit downstream effectors, while others are calcium-dependent enzymes that become catalytically active upon binding calcium.

Key examples span diverse systems. Calmodulin is a primary calcium sensor that activates a family of calcium/calmodulin-dependent kinases (CaMKs) when bound by Ca2+. In plants and some protists, calcium-dependent protein kinases (CDPKs) couple calcium sensing with kinase activity in a single polypeptide. Calcium-dependent phospholipases, such as cPLA2, require Ca2+ for enzymatic activity and play roles in lipid signaling. Calpains are calcium-activated proteases involved in remodeling and signaling. In neurons, calcium triggers exocytosis through sensors like synaptotagmin, facilitating neurotransmitter release; in muscle, calcium-bound calmodulin activates myosin light-chain kinase, promoting contraction. Troponin C in striated muscle binds Ca2+, altering the actin-myosin interaction and enabling contraction.

Physiologically, calcium-dependent processes are tightly regulated in time and space to ensure precise responses. Dysregulation of calcium-dependent signaling is linked to various pathologies, including neurodegenerative diseases, cardiac dysfunction, and inappropriate cell death. The term thus encompasses a broad set of calcium-regulated mechanisms across biology.