摘要
We found that when grown under anaerobic conditions the moderate halophile, gram-positive bacterium Bacillus halodenitrificans (ATCC 49067) synthesizes large amounts of a polypeptide complex that contains a heme center capable of reversibly bind nitric oxide. This complex, when exposed to air, dissociates and reassociates into two active components, a Mn-containing superoxide dismutase (SOD) and a nucleoside diphosphate kinase (BhNDK). The crystal structure of this latter enzyme has been determined at 2.2 Å resolution using molecular replacement method, based on the crystal structure of Drosophilamelanogaster NDK. The model contains 149 residues of a total 150 residues and 34 water molecules. BhNDK consists of a four-stranded antiparallel β-sheet, whose surfaces are partially covered by six α-helices, and its overall andactive site structures are similar to those of homologous enzymes. However, the hexameric packing of BhNDK shows that this enzyme is different from both eukaryotic and gram-negative bacteria. The need for the bacterium to presynthesize both SOD and NDK precursors which are activated during the anaerobic–aerobic transition is discussed.