The TRTK-12 fragment of the F-actin capping protein alpha subunit binds S100B in a calcium dependent manner. S100B undergoes a conformational change that is required for subsequent binding to effector proteins (Inman et al. 2002). S100B is a ligand for AGER (Hofmann et al. 1999). In addition this interaction between S100B andF-actin capping protein alpha could be important for regulating actin filament extension (Ivenkov et al. 1995).