BIOL 194 |
| A class of metalloenzymes known as zinc hydrolases catalyze a variety of important reactions in biology. The enzyme UDP-3-O-((R)-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) catalyzes the first committed step in Lipid A biosynthesis, a critical building block in the outer leaflet of Gram-negative bacteria. LpxC activity has previously been shown to be activated by divalent transition metal ions (Zn(II), Co(II) or Ni(II)) and has been described as a mononuclear zinc protein. Recent evidence suggests that Fe(II) could also be an in vivo catalytic metal ion. The catalytic activity of LpxC reconstituted with Fe(II) under anaerobic conditions is higher than Zn(II)-LpxC and is oxygen sensitive. LpxC purified anaerobically from E. coli exhibits oxygen sensitivity, suggesting Fe(II)-dependent activity. Finally, the metal content, analyzed by ICP-MS, of LpxC purified from E. coli grown in media with low, defined metal concentrations is predominantly iron. However, the iron/zinc ratios in LpxC vary linearly with the iron/zinc ratios in the cell lysate (which depend on the metal content in the media), suggesting that the catalytic metal ion of LpxC varies with cellular conditions. Two interesting possibilities arise from these results – either LpxC lacks specificity for its active-site metal, or the enzyme is subject to a novel regulatory mechanism that is sensitive to intracellular metal concentrations. Preliminary results indicate another metal-dependent deacetylase, human histone deacetylase 8 (HDAC8), may also use Fe(II) as the metal cofactor in vivo, suggesting that this may be a common theme in “zinc”-dependent deacetylases. |
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Enzymes
4:30 PM-6:30 PM, Wednesday, 13 September 2006 Moscone Center -- Hall D, Poster
Sci-Mix
Division of Biological Chemistry |