The binding site of bisphenol A to protein disulphide isomerase

Protein disulphide isomerase (PDI) has been isolated as a binding protein of bisphenol A (BPA) in the rat brain. In this study, we determined binding sites of BPA to PDI and characterized the binding site. First, we identified the BPA-binding domain with ab, b0a0c, a, b, b0 and a0c fragment peptides of PDI by surface plasmon resonance spectroscopy. BPA interacted with ab, b0a 0c, a and b0, suggesting that a and b0 domains are important in their interaction. Second, ab, b0a0c, a,b,b0,a0, abb0a0, abb0, b0a0, "b0 and a0c fragment peptides were used for their isomerase activity with RNase as a substrate. BPA could inhibit the activity of peptide fragments including b0, suggesting that b0 domain contributes to inhibition of catalytic activity of PDI by BPA. Next, we investigated the BPA-binding capacity of PDI by amino acid substitution. PDI lost the BPA-binding activity by the mutation of H258 and mutation of Q245 and N300 also decreased its activity. Furthermore, acidic condition increased the BPA-binding activity of PDI. These results suggest that the charge of these amino acid especially, H258, is important for the BPA to bind to PDI.