Influence of Intrinsic Electric Fields and 2-His-1-Carboxylate/Chloride Facial Triad on the Active Sites of 2-Oxoglutarate–Dependent Enzymes

Iron(II)- and 2-oxoglutarate-dependent (Fe(II)/2OG) oxygenases form a large family of nonheme enzymes containing the Fe(II) center coordinated by two histidine residues and either a carboxylate or halide ligand, with 2OG acting as a cosubstrate. Although these enzymes share a conserved 2-His-1-carboxylate/halide motif in their active sites, they catalyze a wide variety of oxidative chemical reactions. We here investigate two factors that can significantly impact the divergence in their observed catalytic functions, namely, the intrinsic electric field (IEF) exerted on the active site by the surrounding protein environment, and variations of the composition of the facial triad. Concretely, we first evaluate the IEFs in Fe(II)/2OG oxygenases and investigate whether the direction and magnitude of these computed IEFs correlate with catalytic function across multiple subfamilies of Fe(II)/2OG oxygenases. We also examine how these IEFs can influence the geometric and electronic structures of Fe(III)-superoxo intermediates formed in the active site of Fe(II)/2OG oxygenases upon binding O₂, the initial step of their oxidative catalytic cycles. Additionally, we evaluated how the identity and orientation of the third ligand (Glu, Asp, or Cl) in the 2-His-1-carboxylate/halide facial triad influence the active site complexes. Our findings suggest that specific steps in the catalytic cycle are determined by the interplay between the IEF due to the protein environment and the structural features of the facial triad. The results of this study provide insights into the role of IEFs and the facial triads in the observed reaction specificity of different Fe(II)/2OG enzymes.