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Most known nucleotidyl-transfer enzymes use two metal ions for catalysis, but some enzymes use only one divalent cation in their active sites. A comparative analysis of previously available structural data reveals that the one-metal-ion enzymes use a similar mechanism to coordinate their single metal ion, which corresponds, functionally and structurally, to metal ion B in the two-metal-ion enzymes.
The ATPase activity of AAA+ proteins is regulated by their interaction with ligands, but depending on the particular protein it can be stimulated or inhibited, and the mechanism for such control remained unclear. An analysis of previous structural data on various AAA+ proteins now reveals that a conserved glutamate residue adopts two conformations and and thus regulates the ATPase activity.