S-100B: S-100B domain found in proteins similar to S100B. S100B is a calcium-binding protein belonging to a large S100 vertebrate-specific protein family within the EF-hand superfamily of calcium-binding proteins. Note that the S-100 hierarchy, to which this S-100B group belongs, contains only S-100 EF-hand domains, other EF-hands have been modeled separately. S100B is most abundant in glial cells of the central nervous system, predominately in astrocytes. S100B is involved in signal transduction via the inhibition of protein phoshorylation, regulation of enzyme activity and by affecting the calcium homeostasis. Upon calcium binding the S100B homodimer changes conformation to expose a hydrophobic cleft, which represents the interaction site of S100B with its more than 20 known target proteins. These target proteins include several cellular architecture proteins such as tubulin and GFAP; S100B can inhibit polymerization of these oligomeric molecules. Furthermore, S100B inhibits the phosphorylation of multiple kinase substrates including the Alzheimer protein tau and neuromodulin (GAP-43) through a calcium-sensitive interaction with the protein substrates.
Structure:1MHO, Bos taurus holo S100B bound with calcium ions, contacts at 3.5 A
Comment:the N-terminal EF hand is a S100 specific feature while the C-terminal canonical EF hand is similar to the EF hands in calmodulin, troponin C, and parvalbumin
Comment:the second binding site (C-terminal EF hand) has a greater affinity for Ca2+ than the first (N-terminal EF hand)
Jiyao W et al.(2023). "The conserved domain database in 2023.",