Fe(II) /(Alpha)Ketoglutarate‐Dependent Dioxygenase PrhA

Abstract

Nonheme Fe(II)/α‐ketoglutarate (αKG)‐dependent dioxygenases catalyze remarkably diverse reactions, with a single iron ion and αKG as a cofactor and cosubstrate, respectively. Recent studies on fungal meroterpenoid biosynthesis revealed that this class of superfamily enzymes is widely distributed in fungal genomes and plays a pivotal role in the structural diversification and complexation of secondary metabolites. For example, PrhA, the nonheme Fe(II)/αKG‐dependent dioxygenase involved in the biosynthesis of paraherquonin, is one of the first structurally and mechanistically characterized enzymes in the fungal polyketide‐terpenoid hybrid biosynthetic pathway. Structural and functional studies have revealed that only three amino acid residues lining the active site cavity are responsible for the complete switch in the enzyme reactions, from the C‐5/C‐6 desaturation and the ring‐expanded cycloheptadiene formation to the C‐1/C‐2 desaturation and spirolactone ring contraction. The subtle change of the active site architecture results in different distances of the reactive atoms relative to the active ferryl‐oxo center during the enzyme reaction. PrhA thus represents an intriguing platform for the structure‐based engineering of the nonheme Fe(II)/αKG‐dependent multifunctional dioxygenases.

Engineering Fe(II)/α-Ketoglutarate-Dependent Halogenases and Desaturases

“…In this context, a further desirable target chemistry is the non-α-heteroatom-assisted desaturation of C–C units in complex molecular structures (Figure B). This reaction has been reported for only a small selection of α-ketoglutarate-dependent dioxygenases acting on their native substrate (PrhA, ,, BcmF, and KabC), whereas VioC and clavaminate synthase (CS) have been observed to exhibit non-α-heteroatom-assisted desaturation activity in addition to hydroxylation activity when acting on non-native compounds (Table and Figure B). Although the α-ketoglutarate-dependent desaturases mentioned above have been submitted to mechanistic studies, the molecular details of α-KGD-catalyzed olefin installation remain less well understood than those of the corresponding hydroxylations …”