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. May also play a role in suppressing tumor cell growth (By similarity). Homodimer. Interacts with FKBP4. Interacts with PPP5C (via TPR repeats); the interaction is calcium-dependent and modulates PPP5C activity (By similarity). Interacts with TPPP; this interaction inhibits TPPP dimerization (By similarity). This protein binds two calcium ions. Belongs to the S-100 family.