Catalytic metal ion switching in zinc‐dependent deacetylases

Abstract

The metallohydrolase UDP‐3‐O‐((R)‐3‐hydroxymyristoyl)‐N‐acetylglucosamine deacetylase (LpxC) catalyzes the first committed step in Lipid A biosynthesis, a critical component of the outer leaflet of gram‐negative bacteria. LpxC activity has previously been shown to be activated by a divalent transition metal ion (Zn(II), Co(II), or Ni(II)) and has been described as a mononuclear zinc enzyme. Fe(II) has not yet been considered as the in vivo catalytic metal ion. However, LpxC reconstituted with Fe(II) exhibits increased catalytic activity vs. Zn(II) and the activity of LpxC in E. coli cell extracts is oxygen‐sensitive. When LpxC is purified anaerobically from E. coli grown in media with defined metal concentrations, the ratio of iron/zinc bound to LpxC varies linearly with the iron/zinc ratio in the cell lysate, suggesting that the catalytic metal ion of LpxC depends on the cellular conditions. Binding of Fe2+ vs. Zn2+ has been measured and compared to free cellular metal concentrations. Two possibilities arise from these results – either LpxC lacks specificity for its active site metal, or the enzyme is subject to a regulatory mechanism that responds to intracellular metal concentrations. Preliminary results indicate another Zn‐dependent deacetylase, human histone deacetylase 8 (HDAC8), may also be able to use Fe(II) in vivo, suggesting this may be a broader theme in “zinc”‐dependent deacetylases.