Functional site prediction of BRCT domain containing phosphate binding pocket

The BRCT domain (after the C-terminal domain of a breast cancer susceptibility protein) is an important signaling and protein targeting motif in the DNA damage response system. To clarify possible interaction mechanisms between the BRCT domain, which contains phosphate binding pocket and its phosphorylated ligand, we analyzed the structural conservation and electrostatic surface potentials of XRCC1 BRCT1, PTIP BRCT4, ECT2 BRCT1 and TopBP1 BRCT1. The results showed common structurally conserved and positively charged grooves located around the phosphate binding pockets of these domains. These grooves possibly act as functional sites in the four BRCT domains due to the extensive existence of similar grooves in the BRCT domains containing phosphate binding pocket. The two sides of the groove were composed of positively charged and hydrophilic residues and the bottom was composed of hydrophobic and hydrophilic residues, suggesting that the groove binds to BRCT domain ligand mainly through electrostatic and hydrophobic interactions. The groove was mainly located in individual BRCT domains and differences in shape and charge distribution among the four BRCT domain grooves were observed, indicating that ligand binding specificity was predominantly determined by individual BRCT domains. The groove was centered by the phosphate binding pocket, implying that the groove interacted with residues located at both the N-terminal and C-terminal sides of the phosphorylated residue.