title: A complex iron-calcium cofactor catalyzing phosphotransfer chemistry.
abstract: 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.
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
authors.forename: Shee Chien
authors.initials: SC
authors.lastname: Yong
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, United Kingdom.
authors.forename: Pietro
authors.initials: P
authors.lastname: Roversi
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, United Kingdom.
authors.forename: James
authors.initials: J
authors.lastname: Lillington
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
authors.forename: Fernanda
authors.initials: F
authors.lastname: Rodriguez
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
authors.forename: Martin
authors.initials: M
authors.lastname: Krehenbrink
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
authors.forename: Oliver B
authors.initials: OB
authors.lastname: Zeldin
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
authors.forename: Elspeth F
authors.initials: EF
authors.lastname: Garman
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, United Kingdom.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Lea
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
authors.forename: Ben C
authors.initials: BC
authors.lastname: Berks
mesh_terms: D000469:Alkaline Phosphatase / Q000737:chemistry* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002118:Calcium / Q000737:chemistry*; D002384:Catalysis; D020134:Catalytic Domain; D003067:Coenzymes / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D010710:Phosphates / Q000378:metabolism*; D017433:Protein Structure, Secondary; D011551:Pseudomonas fluorescens / Q000201:enzymology; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D003067:Coenzymes; D008024:Ligands; D010710:Phosphates; D011994:Recombinant Proteins; D007501:Iron; D000469:Alkaline Phosphatase; D002118:Calcium