Cobalt-, zinc- and iron-bound forms of adenylate kinase (AK) from the sulfate-reducing bacterium Desulfovibrio gigas: purification, crystallization and preliminary X-ray diffraction analysis

Adenylate kinase (AK; ATP:AMP phosphotransferase; EC 2.7.4.3) is involved in the reversible transfer of the terminal phosphate group from ATP to AMP. AKs contribute to the maintenance of a constant level of cellular adenine nucleotides, which is necessary for the energetic metabolism of the cell. Three metal ions, cobalt, zinc and iron(II), have been reported to be present in AKs from some Gram-negative bacteria. Native zinc-containing AK from Desulfovibrio gigas was purified to homogeneity and crystallized. The crystals diffracted to beyond 1.8 angstrom resolution. Furthermore, cobalt-and iron-containing crystal forms of recombinant AK were also obtained and diffracted to 2.0 and 3.0 angstrom resolution, respectively. Zn2+-AK and Fe2+-AK crystallized in space group I222 with similar unit-cell parameters, whereas Co2+-AK crystallized in space group C2; a monomer was present in the asymmetric unit for both the Zn2+-AK and Fe2+-AK forms and a dimer was present for the Co2+-AK form. The structures of the three metal-bound forms of AK will provide new insights into the role and selectivity of the metal in these enzymes.