A New Member of the Alkaline Phosphatase Superfamily with a Formylglycine Nucleophile: Structural and Kinetic Characterisation of a Phosphonate Monoester Hydrolase/Phosphodiesterase from Rhizobium Leguminosarum.Jonas, S., Van Loo, B., Hyvonen, M., Hollfelder, F.
(2008) J Mol Biol 384: 120
- PubMed: 18793651
- DOI: https://doi.org/10.1016/j.jmb.2008.08.072
- Primary Citation of Related Structures:
- PubMed Abstract:
The alkaline phosphatase superfamily comprises a large number of hydrolytic metalloenzymes such as phosphatases and sulfatases. We have characterised a new member of this superfamily, a phosphonate monoester hydrolase/phosphodiesterase from Rhizobium leguminosarum (R/PMH) both structurally and kinetically. The 1.42 A crystal structure shows structural homology to arylsulfatases with conservation of the core alpha/beta-fold, the mononuclear active site and most of the active-site residues. Sulfatases use a unique formylglycine nucleophile, formed by posttranslational modification of a cysteine/serine embedded in a signature sequence (C/S)XPXR. We provide mass spectrometric and mutational evidence that R/PMH is the first non-sulfatase enzyme shown to use a formylglycine as the catalytic nucleophile. R/PMH hydrolyses phosphonate monoesters and phosphate diesters with similar efficiency. Burst kinetics suggest that substrate hydrolysis proceeds via a double-displacement mechanism. Kinetic characterisation of active-site mutations establishes the catalytic contributions of individual residues. A mechanism for substrate hydrolysis is proposed on the basis of the kinetic data and structural comparisons with E. coli alkaline phosphatase and Pseudomonas aeruginosa arylsulfatase. R/PMH represents a further example of conservation of the overall structure and mechanism within the alkaline phosphatase superfamily.
Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB21GA, UK.