Crystal structures of human prostatic acid phosphatase in complex with a phosphate ion and α-benzylaminobenzylphosphonic acid update the mechanistic picture and offer new insights into inhibitor design

The X-ray crystal structure of human prostatic acid phosphatase (PAP) in complex with a phosphate ion has been determined at 2.4 Angstrom resolution. This structure offers a snapshot of the final intermediate in the catalytic mechanism and does not support the role of Asp 258 as a proton donor in catalysis. A total of eight hydrogen bonds serve to strongly bind the phosphate ion within the active site. Bound PEG molecules from the crystallization matrix have allowed the identification of a channel within the molecule that likely plays a role in molecular recognition and in macromolecular substrate selectivity. Additionally, the structure of PAP in complex with a phosphate derivative, alpha-benzylaminobenzylphosphonic acid, a potent inhibitor (IC50 = 4 nM), has been determined to 2.9 Angstrom resolution. This structure gives new insight into the determinants of binding hydrophobic ligands within the active site and allows us to explain PAP's preference for aromatic substrates.