Specificity and Zn2+ enhancement of the S100B binding epitope TRTK-12

The calcium-binding protein S100B (an S100 dimer composed of two S100 beta monomers) is proposed to act as a calcium-sensory protein through interacti ons with a variety of proteins. While the nature of the exact targets for S 100B has yet to be defined, random bacteriophage peptide mapping experiment s have elucidated a calcium-sensitive "epitope" (TRTK-12) for S100B recogni tion. In this work, interactions of TRTK-12 with S100B have been shown to b e calcium-sensitive. In addition, the interactions are enhanced by zinc bin ding to S100B, resulting in an approximate 5-fold decrease in the TRTK-12/S 100B dissociation constant. Moreover, Zn2+ binding alone has little effect. TRTK-12 showed Little evidence for binding to another S100 protein, S100A1 1 or to a peptide derived from the N terminus of S100B, indicating both a l evel of specificity for TRTK-12 recognition by S100B and that the N-termina l region of S100B is probably not involved in protein-protein interactions. NMR spectroscopy revealed residues most responsive to TRTK-12 binding that could be mapped to the surface of the three-dimensional structure of calci um-saturated S100B, revealing a common region indicative of a binding site.