Abstract
Flavin-dependent monooxygenases (FMOs) are ancient enzymes present in all kingdoms of life. FMOs typically catalyze the incorporation of an oxygen atom from molecular oxygen into small molecules. To date, the majority of functional characterization studies have been performed on mammalian, fungal and bacterial FMOs, showing that they play fundamental roles in drug and xenobiotic metabolism. By contrast, our understanding of FMOs across the plant kingdom is very limited, despite plants possessing far greater FMO diversity compared to both bacteria and other multicellular organisms. Here, we review the progress of plant FMO research, with a focus on FMO diversity and functionality. Significantly, of the FMOs characterized to date, they all perform oxygenation reactions that are crucial steps within hormone metabolism, pathogen resistance, signaling and chemical defense. This demonstrates the fundamental role FMOs have within plant metabolism, and presents significant opportunities for future research pursuits and downstream applications.
Highlights
Flavin-dependent monooxygenases (FMOs; EC 1.14.13.8) constitute a large group of ancient enzymes that are present in all kingdoms of life
This review aims to summarize the diversity and role of characterized plant FMOs
Plant Class B FMOs have three conserved motifs (Figure 1A): The FAD-binding motif (GXGXXG), the NADPH-binding motif (GXGXXG) and the FMO-identifying sequence motif (FXGXXXHXXXY/F) [29]. This FMO-identifying sequence motif is not directly connected to the active site, but rather it acts as a linker section between the FAD and NADPH binding pockets, ensuring correct domain rotations and conformational changes [32]. These motifs are present in plant Baeyer-Villiger monooxygenases (BVMOs) and BFMOs known to date, the motifs can be localized at different positions (Figure 1A)
Summary
Flavin-dependent monooxygenases (FMOs; EC 1.14.13.8) constitute a large group of ancient enzymes that are present in all kingdoms of life. Other oxygenase enzymes, such as cytochromes P450 (CYPs), have received comparatively more attention for their endogenous roles in vivo [7,8,9], and in regard to the identification and development of new enzyme reactions This is surprising considering FMOs possess a number of advantageous properties compared to CYPs, especially for downstream biotechnological applications. In 2007, a detailed review of plant FMOs by Schlaich et al [21] concluded that for the field to progress “it is necessary to first identify the endogenous substrates” This insight has proven to be correct, and, at present, only a small handful of plant FMOs have been characterized and the endogenous substrates for plant FMOs still largely remain unknown. We seek to highlight the opportunities of FMO research for the forthcoming years to maximize the potential of FMOs for future downstream applications
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