Identification and biochemical characterization of a unique Mn2+-dependent UMP kinase from Helicobacter pylori

Uridine monophosphate (UMP) kinase converts UMP to the corresponding UDP in the presence of metal ions and ATP and is allosterically regulated by nucleotides such as UTP and GTP. Although the UMP kinase reported to date is Mg2+-dependent, we found in this study that the UMP kinase of Helicobacter pylori had a preference for Mn2+ over Mg2+, which may be related to a conformational difference between the Mn2+-bound and Mg2+-bound UMP kinase. Similar to previous findings, the UMP kinase activity of H. pylori UMP kinase was inhibited by UTP and activated by GTP. However, a relatively low GTP concentration (0.125 mM) was required to activate H. pylori UMP kinase to a level similar to other bacterial UMP kinases using a higher GTP concentration (0.5 mM). In addition, depending on the presence of either Mg2+ or Mn2+, a significant difference in the level of GTP activation was observed. It is therefore hypothesized that the Mg2+-bound and Mn2+-bound H. pylori UMP kinase may be activated by GTP through different mechanisms.