The Effects of CapZ Peptide (TRTK-12) Binding to S100B-Ca(2+) as Examined by NMR and X-ray CrystallographyCharpentier, T.H., Thompson, L.E., Liriano, M.A., Varney, K.M., Wilder, P.T., Pozharski, E., Toth, E.A., Weber, D.J.
(2010) J.Mol.Biol. 396: 1227-1243
- PubMed: 20053360
- DOI: 10.1016/j.jmb.2009.12.057
- Primary Citation of Related Structures:
- PubMed Abstract:
Structure-based drug design is underway to inhibit the S100B-p53 interaction as a strategy for treating malignant melanoma. X-ray crystallography was used here to characterize an interaction between Ca(2)(+)-S100B and TRTK-12, a target that binds to ...
Structure-based drug design is underway to inhibit the S100B-p53 interaction as a strategy for treating malignant melanoma. X-ray crystallography was used here to characterize an interaction between Ca(2)(+)-S100B and TRTK-12, a target that binds to the p53-binding site on S100B. The structures of Ca(2+)-S100B (1.5-A resolution) and S100B-Ca(2)(+)-TRTK-12 (2.0-A resolution) determined here indicate that the S100B-Ca(2+)-TRTK-12 complex is dominated by an interaction between Trp7 of TRTK-12 and a hydrophobic binding pocket exposed on Ca(2+)-S100B involving residues in helices 2 and 3 and loop 2. As with an S100B-Ca(2)(+)-p53 peptide complex, TRTK-12 binding to Ca(2+)-S100B was found to increase the protein's Ca(2)(+)-binding affinity. One explanation for this effect was that peptide binding introduced a structural change that increased the number of Ca(2+) ligands and/or improved the Ca(2+) coordination geometry of S100B. This possibility was ruled out when the structures of S100B-Ca(2+)-TRTK-12 and S100B-Ca(2+) were compared and calcium ion coordination by the protein was found to be nearly identical in both EF-hand calcium-binding domains (RMSD=0.19). On the other hand, B-factors for residues in EF2 of Ca(2+)-S100B were found to be significantly lowered with TRTK-12 bound. This result is consistent with NMR (15)N relaxation studies that showed that TRTK-12 binding eliminated dynamic properties observed in Ca(2+)-S100B. Such a loss of protein motion may also provide an explanation for how calcium-ion-binding affinity is increased upon binding a target. Lastly, it follows that any small-molecule inhibitor bound to Ca(2+)-S100B would also have to cause an increase in calcium-ion-binding affinity to be effective therapeutically inside a cell, so these data need to be considered in future drug design studies involving S100B.
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 North Greene Street, Baltimore, MD 21201, USA.