s100

S100 refers to a family of low-molecular-weight, calcium-binding proteins present in many vertebrate cell types. Members are characterized by EF-hand motifs and typically form homodimers or heterodimers, with molecular weights around 10–12 kDa. In humans, the family comprises more than 20 members, many encoded in a gene cluster on chromosome 1q21, though additional members occur at other loci. S100 proteins function as intracellular signaling molecules, influencing processes such as cytoskeletal dynamics, enzyme activity, cell growth, differentiation, and gene regulation. Some family members localize to the nucleus or are secreted, where they can participate in extracellular signaling.

Functionally, S100 proteins respond to changes in intracellular calcium, undergoing conformational changes that enable interactions with target proteins and regulate diverse pathways. They can act as calcium sensors and modulators of signaling networks within the cell. Extracellularly, certain S100 proteins act as damage-associated molecular patterns and engage receptors such as RAGE and Toll-like receptors to promote inflammatory responses. They can be released passively from damaged cells or actively secreted by immune or tumor cells. Expression and function are highly context-dependent, with tissue- and disease-specific roles.

Clinical relevance and research use stem from their stability and distinctive expression patterns. S100 proteins serve as biomarkers in various conditions; for example, S100B is associated with brain injury and astrocyte activity, while the S100A8/S100A9 complex (calprotectin) marks neutrophil activation and inflammatory disease. In oncology, certain S100 family members correlate with tumor progression and metastatic potential in a context-dependent manner. Detection methods include immunohistochemistry and immunoassays in bodily fluids, supporting diagnostic and prognostic applications.