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Alkaline phosphatases play a crucial role in phosphate acquisition by microorganisms. To expand our understanding of catalysis by this class of enzymes, we have determined the structure of the widely occurring microbial alkaline phosphatase PhoX. The enzyme contains a complex active-site cofactor comprising two antiferromagnetically coupled ferric iron ions (Fe(3+)), three calcium ions (Ca(2+)), and an oxo group bridging three of the metal ions. Notably, the main part of the cofactor resembles synthetic oxide-centered triangular metal complexes. Structures of PhoX-ligand complexes reveal how the active-site metal ions bind substrate and implicate the cofactor oxo group in the catalytic mechanism. The presence of iron in PhoX raises the possibility that iron bioavailability limits microbial phosphate acquisition.

Original publication

DOI

10.1126/science.1254237

Type

Journal article

Journal

Science

Publication Date

05/09/2014

Volume

345

Pages

1170 - 1173

Keywords

Alkaline Phosphatase, Bacterial Proteins, Calcium, Catalysis, Catalytic Domain, Coenzymes, Iron, Ligands, Phosphates, Protein Structure, Secondary, Pseudomonas fluorescens, Recombinant Proteins