Structure-activity relationship studies to probe the phosphoprotein binding site on the carboxy terminal domains of the breast cancer susceptibility gene 1

Abstract

Carboxy terminal BRCT domains of the breast cancer susceptibility gene 1 (BRCA1) bind to phosphorylated proteins through a pSXXF consensus recognition motif. We report a systematic structure-activity relationship study that maps the BRCT(BRCA1)-pSXXF binding interface, leading to identification of peptides with nanomolar binding affinities comparable to those of the previously reported 13-mer peptides and providing a clear description of the pSXXF-BRCT interface, which is essential for developing small molecule inhibitors via the peptidomimetic approach.

Figure 1

A and B are two orientations of the pSPTF-BRCT(BRCA1) binding interface. The tetrapeptide is shown as green sticks while the protein is shown in blue. The potential hydrophilic contacts are shown by broken dotted lines and the hydrophobic contacts are shown either as surface or by dots. The red double headed arrow shows the contact made by the β-carbon on pSer with the Thr₁₇₀₀ side chain on BRCT. (PDB ID: 1T29)

Figure 2

Thermodynamic optimization plot (TOP): The optimization line was generated using two experimental data points (-TΔS, ΔH) and (0, ΔG) for peptide 1. Horizontal and vertical lines were drawn through the (-TΔS, ΔH) data point of peptide 1 to establish the six regions labeled I to VI. Peptides that fall in regions I, V and VI result in the gain of binding affinity while those that fall in regions II, III and IV result in loss of binding affinity.

Figure 3

(A) Graphical representation of the thermodynamic parameters of the pSPXF peptides. (B) Representative binding isotherm of peptide 18.