Linear polyphosphate chains have been found to play a key role in bacterial responses to stresses and nutritional depletion, and are necessary for host infection of various pathogens. Polyphosphate kinase (PPK) is a critical enzyme responsible for polyphosphate synthesis in bacteria. PPK knockout mutations in several Gram-negative pathogens identify PPK as an ideal drug target for the development of a new class of antibacterial drugs. To reveal the catalytic mechanism and provide a structural basis for drug discovery, we have purified and crystallized full-length Escherichia coli PPK and its complex with AMP-PNP. The crystals diffract to a resolution of 2.5 Angstrom and belong to the space group P4(2)2(1)2 with unit-cell parameters a = 152.0, b = 152.0, and c = 150.0 Angstrom. Crystal structure of PPK is being determined by the Se-Met MAD experiment. (C) 2003 Elsevier Science (USA). All rights reserved.