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Catalytic Core of a Membrane-Associated Eukaryotic Polyphosphate Polymerase

Science  24 Apr 2009:
Vol. 324, Issue 5926, pp. 513-516
DOI: 10.1126/science.1168120

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Abstract

Polyphosphate (polyP) occurs ubiquitously in cells, but its functions are poorly understood and its synthesis has only been characterized in bacteria. Using x-ray crystallography, we identified a eukaryotic polyphosphate polymerase within the membrane-integral vacuolar transporter chaperone (VTC) complex. A 2.6 angstrom crystal structure of the catalytic domain grown in the presence of adenosine triphosphate (ATP) reveals polyP winding through a tunnel-shaped pocket. Nucleotide- and phosphate-bound structures suggest that the enzyme functions by metal-assisted cleavage of the ATP γ-phosphate, which is then in-line transferred to an acceptor phosphate to form polyP chains. Mutational analysis of the transmembrane domain indicates that VTC may integrate cytoplasmic polymer synthesis with polyP membrane translocation. Identification of the polyP-synthesizing enzyme opens the way to determine the functions of polyP in lower eukaryotes.

  • * Present address: Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK.

  • Present address: Novartis Pharma Schweiz AG, Monbijoustrasse 118, 3007 Bern, Switzerland.

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