THE 2-HIS-1-CARBOXYLATE FACIAL TRIAD - AN EMERGING STRUCTURAL MOTIF IN MONONUCLEAR NONHEME IRON(II) ENZYMES

A 2-His-1-carboxylate facial triad is a common feature of the active s ites in a number of mononuclear non-heme iron(II) enzymes. This struct ural motif was established crystallographically for five different cla sses of enzymes and inferred from sequence similarity for two other cl asses. The 2-His-1-carboxylate facial triad anchors the iron in the ac tive site and at the same time maintains three additional cis-oriented sites. These sites can be used to bind other endogenous ligands or ex ogenous ligands such as substrate and/or O-2, giving the metal center great flexibility to use different mechanistic strategies to perform a variety of chemical transformations.