May function as calcium sensor and modulator, contributing to cellular calcium signaling. May function by interacting with other proteins, such as TPR-containing proteins, and indirectly play a role in many physiological processes such as the reorganization of the actin cytoskeleton and in cell motility. Binds 2 calcium ions. Calcium binding is cooperative (By similarity). Homodimer; head to tail assembly of 2 subunits. Interacts with CACYBP in a calcium-dependent manner. Interacts with ANXA2 and ANXA11 (via N-terminus). Interacts with SUGT1. Interacts with TP53; has higher affinity for TP53 that is phosphorylated on its N-terminal domain, and lower affinity for TP53 that is phosphorylated on its C-terminal domain. Interacts with tropomyosin. Interacts with FKBP4. 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). This protein co-purified with the prolactin receptor. Belongs to the S-100 family.