Weakly binds calcium but binds zinc very tightly-distinct binding sites with different affinities exist for both ions on each monomer. Physiological concentrations of potassium ion antagonize the binding of both divalent cations, especially affecting high-affinity calcium-binding sites. Binds to and initiates the activation of STK38 by releasing autoinhibitory intramolecular interactions within the kinase. Interaction with AGER after myocardial infarction may play a role in myocyte apoptosis by activating ERK1/2 and p53/TP53 signaling. Could assist ATAD3A cytoplasmic processing, preventing aggregation and favoring mitochondrial localization. May mediate calcium-dependent regulation on many physiological processes by interacting with other proteins, such as TPR-containing proteins, and modulating their activity (By similarity). Dimer of either two alpha chains, or two beta chains, or one alpha and one beta chain. The S100B dimer binds two molecules of STK38. Interacts with CACYBP in a calcium-dependent manner. Interacts with ATAD3A; this interaction probably occurs in the cytosol prior to ATAD3A mitochondrial targeting. Interacts with S100A6. The S100B dimer interacts with two molecules of CAPZA1. Interacts with AGER. Interacts with PPP5C (via TPR repeats); the interaction is calcium-dependent and modulates PPP5C activity. Interacts with TPPP; this interaction inhibits TPPP dimerization (By similarity). Belongs to the S-100 family.