PinA from Aspergillus nidulans binds to pS/pT-P motifs using the same Loop I and XP groove as mammalian Pin1

Binding of the Cdc25c-T48 ligand to PinA from Aspergillus nidulans has been characterised by the identification of 15N and 1H resonances from 1H– 15N HSQC NMR titration experiments using previous backbone assignments. It is shown that the binding site for the Cdc25c-T48 ligand with PinA is the same as in the mammalian protein Pin1, although with a reduced binding affinity. It had previously been proposed that the arginine residue (R17) in the loop I region of the Pin1 WW domain is essential for binding to the pSer/pThr-Pro motifs of phosphorylated ligands such as Cdc25c. In PinA, a fungal homologue of Pin1, the arginine residue (R17) is replaced with an asparagine residue (N17). The effect of substitution of R17 by N17 in Pin1 has been investigated via a computational study, which predicted that changing R17 to N17 in Pin1 lowers the ligand binding affinity as a result of reduced hydrogen bonding between the protein and the phosphate group of the ligand.