S-100αα (S-100aa) from bovine brain is a low molecular weight, cytoplasmic, calcium-binding protein belonging to the S100 family, which is characterized by the presence of EF-hand calcium-binding motifs. Structurally, S-100αα is a homodimer composed of two alpha subunits, distinct from the beta-beta (S-100ββ) and alpha-beta (S-100αβ) forms found in nervous tissue. Its conformation and function are modulated by calcium and, to a lesser extent, by other ions such as potassium, reflecting its role in responding to changes in the cellular environment.

Functionally, S-100αα participates in the regulation of various intracellular activities, including cell proliferation, differentiation, and cytoskeletal dynamics, often through interactions with target proteins in a calcium-dependent manner. It is predominantly expressed in astroglial cells and is involved in maintaining neural homeostasis. Aberrant expression or release of S-100 proteins, including S-100αα, has been linked to neurological diseases such as Alzheimer's disease, stroke, and traumatic brain injury, where their serum levels serve as sensitive biomarkers of brain damage and disease progression.

In research and clinical applications, S-100αα is widely used as a marker for central nervous system injury and as a tool for studying calcium-mediated signaling pathways in neurobiology. Its measurement aids in diagnosis, prognosis, and monitoring of neurological disorders and has potential utility in cancer and inflammatory disease research due to the broader roles of S100 proteins in cell regulation and disease pathogenesis.