Biochemie und analytische Biochemie

Abstrakt

Opposite Regulatory Effects of Iron Ions on the In Vitro Catalytic Activities of Nare, the Toxin-like ADP-Ribosyltransferase from Neisseria meningitides

Mariangela Del Vecchio and Enrico Balducci

NarE, the mono ADP-ribosyltransferase identified in Neisseria meningitidis, catalyzes three enzymatic reactions. NarE transfers a single ADP-ribose unit to guanidine compounds, hydrolyses NAD in nicotinamide and free ADP-ribose, and ADP-ribosylates itself. We have previously shown that NarE contains an iron-sulfur cluster by biophysical and biochemical analyses. The presence of a structured and stable iron-sulfur cluster is essential for ADP-ribosyltransferase but not for NAD-glycohydrolase activity. We report here that ferric, but not ferrous, ions stimulated the ADPribosyltransferase activity. On the contrary ferrous, but not ferric, ions activated NAD-glycohydrolase activity. These iron effects were reversed when enzymatic reactions were run in the presence of the iron-chelator O-phenantroline. In the presence of either ferric or ferrous ions there was an increase of the Vmax both for transferase and NADase activity while the Km value for NAD was unaltered. The presence of 10 mM Fe3+ increased the ADP-ribosyltransferase activity when we mutated residues not involved in cluster, while is ineffective when residues involved in cluster are mutated. Similar results were obtained with NAD-glycohydrolase activity. The results presented here demonstrate that iron, which plays an important role in metabolism, can modulate NarE activities depending on its oxidation state. This novel observation could be relevant in the context of Neisseria meningitidis infection.