Rieske Oxygenases and Other Ferredoxin‐Dependent Enzymes: Electron Transfer Principles and Catalytic Capabilities

Abstract

Enzymes that depend on sophisticated electron transfer via ferredoxins (Fds) exhibit outstanding catalytic capabilities, but despite decades of research, many of them are still not well understood or exploited for synthetic applications. This review aims to provide a general overview of the most important Fddependent enzymes and the electron transfer processes involved. While several examples are discussed, we focus in particular on the family of Rieske non-heme iron-dependent oxygenases (ROs). In addition to illustrating their electron transfer principles and catalytic potential, the current state of knowledge on structure-function relationships and the mode of interaction between the redox partner proteins is reviewed. Moreover, we highlight several key catalyzed transformations, but also take a deeper dive into their engineerability for biocatalytic applications. The overall findings from these case studies highlight the catalytic capabilities of these biocatalysts and could stimulate future interest in developing additional Fddependent enzyme classes for synthetic applications.

Rieske Oxygenase-Catalyzed Oxidative Late-Stage Functionalization during Complex Antifungal Polyketide Biosynthesis

“…To exclude degradation of the thioesters and their oxidation products in the E. coli , the bioconversions were repeated in the presence of the β-oxidation inhibitor 4-pentynoic acid, leading to the same result . While it seems obvious that the ACP-attachment of PKS intermediates represents a relevant structural deviation that affects the enzymatic activity of JerL and JerP, their inactivity toward projerangolid ( 9 ) might seem surprising but falls in line with a narrow substrate scope that has been observed for ROs before . When purified JerF or jerF expression lysate were added to the bioconversions of 9 with JerO/L and JerO/P, product formation was restored, giving 12 and 13 as in the direct bioconversions of 10 with the individual ROs.…”

“…19 Numerous ROs that catalyze degradative reactions in catabolic pathways have been biochemically characterized, often accompanied by X-ray crystal structure analysis. 15 Catabolic arene dioxygenases are, for example, also frequently applied for biocatalytic cis-dihydroxylation of arenes and olefins. 20,21 ROs from microbial natural product biosynthetic pathways are involved in a remarkable array of oxidative transformations.…”

“…ROs are known to catalyze challenging oxidative transformations and to have a catalytic repertoire similar to that of cytochrome P450 enzymes . ROs have a catalytic non-heme iron center and are regenerated by a complex electron transport chain (ETC) that minimally consists of a flavin-dependent reductase (FDR). , The FDR transfers two electrons from NAD­(P)­H, directly or via a ferredoxin, to the RO’s [2Fe-2S] cluster, which is ligated by two His and two Cys residues.…”

“…39 While it seems obvious that the ACP-attachment of PKS intermediates represents a relevant structural deviation that affects the enzymatic activity of JerL and JerP, their inactivity toward projerangolid (9) might seem surprising but falls in line with a narrow substrate scope has been observed for ROs before. 15 When purified JerF or jerF expression lysate were added to the bioconversions of 9 with JerO/L and JerO/P, product formation was restored, giving 12 and 13 as in the direct bioconversions of 10 with the individual ROs. This highlights the importance of the methylenolether for both RO-catalyzed oxidations and casts a clear light on the biosynthetic timing.…”

“…ROs take part in catabolic and biosynthetic pathways . Numerous ROs that catalyze degradative reactions in catabolic pathways have been biochemically characterized, often accompanied by X-ray crystal structure analysis . Catabolic arene dioxygenases are, for example, also frequently applied for biocatalytic cis -dihydroxylation of arenes and olefins. , ROs from microbial natural product biosynthetic pathways are involved in a remarkable array of oxidative transformations. , The activity of ROs in a THP-forming desaturation–epoxidation cascade (MupW; mupirocin biosynthesis), in multiple hydroxylations of sp 3 carbons (SxtT, SxtH, and GxtA; saxitoxin biosynthesis), in oxidative cyclization (RedG and MarG; prodiginine alkaloid biosynthesis) , and in N -oxidation (PrnD and AuaF; aminopyrrolnitrin/aurachin biosynthesis) , has been experimentally confirmed, and numerous others have been proposed .…”