PMID: 19469484

Authors:

Charpentier TH, Wilder PT, Liriano MA, Varney KM, Zhong S, Coop A, Pozharski E, Mackerell AD, Toth EA, Weber DJ

Title:

Small molecules bound to unique sites in the target protein binding cleft of calcium-bound S100B as characterized by nuclear magnetic resonance (NMR) and X-ray crystallography.

Journal:

Biochemistry. 2009 May 26.

Abstract:

Structural studies are part of a rational drug design program underway to inhibit the S100B-p53 interaction and restore wild-type p53 function in malignant melanoma. To this end, structures of three compounds (SBi132, SBi1279, and SBi523) bound to Ca²⁺-S100B were determined by X-ray crystallography at 2.10 A (Rfree = 0.257), 1.98 A (Rfree = 0.281) and 1.90 A (Rfree = 0.228) resolution, respectively. Upon comparison, SBi132, SBi279, and SBi523 were found to bind in distinct locations/orientations within the hydrophobic target binding pocket of Ca²⁺-S100B with minimal structural changes observed for the protein upon complex formation with each compound. Specifically, SBi132 binds nearby residues in loop 2 (His-42, Phe-43, Leu-44) and helix 4 (Phe-76, Met-79, Ile-80, Ala-83, Cys-84, Phe-87 and Phe-88); whereas, SBi523 interacts with a separate site defined by residues within loop 2 (Ser-41, His-42, Phe-43, Leu-44, Glu-45 and Glu-46) and one residue on helix 4 (Phe-87). The SBi279 binding site on Ca²⁺-S100B overlaps the SBi132 and SBi523 sites and contacts residues in both loop 2 (Ser-41, His-42, Phe-43, Leu-44, Glu-45) and helix 4 (Ile-80, Ala-83, Cys-84, Phe-87 and Phe-88). NMR data, including saturation transfer difference (STD) and ¹⁵N backbone and ¹³C sidechain chemical shift perturbations were consistent with the X-ray crystal structures and demonstrated the relevance of all three small molecule-S100B complexes in solution. The discovery that SBi132, SBi279, and SBi523 bind to proximal sites on Ca²⁺-S100B could be useful for the development of a new class of molecule(s) that interacts with one or more of these binding sites simultaneously, thereby by yielding novel tight binding inhibitors specific for blocking protein-protein interactions involving S100B.