Correspondence on "Structural Insight into the Catalytic Mechanism of the Endoperoxide Synthase FtmOx1"

Abstract

In their recent Angewandte Chemie publication (doi: 10.1002/anie.202112063), Cen, Wang, Zhou et al. reported the crystal structure of a ternary complex of the non-heme iron endoperoxidase FtmOx1 (PDB entry 7ETK). The biochemical data assessed in this study were from a retracted study (doi: 10.1038/nature15519) by Zhang, Liu, Zhang et al.; no additional biochemical data were included, yet there was no discussion on the source of the biochemical data in the report by Cen, Wang, Zhou et al. Based on this new crystal structure and subsequent QM/MM-MD calculations, Cen, Wang, Zhou et al. concluded that their work provided evidence supporting the CarC-like mechanistic model for FtmOx1 catalysis. However, the authors did not accurately describe either the CarC-like model or the COX-like model, and they did not address the differences between them. Further, and contrary to their interpretations in the manuscript, the authors' data are consistent with the COX-like model once the details of the CarC-like and COX-like models have been carefully analyzed.

Keywords: Biosynthesis; Endoperoxides; FtmOx1; Iron; Non-heme enzymes.

Figure 1.

Key FtmOx1 structural information. A) and B) Structures of the FtmOx1·Fe^II·αKG binary complex (PDB entry 4Y5S, A) and the FtmOx1·Fe^II·αKG·1 ternary complex (PDB entry 7ETK, B). The metallo-center and surrounding residues are shown in sphere and stick representation, respectively. Polar interactions within these residues are shown as black dashed lines. C) Details of the positions of Y224, Y68, and the substrate fumitremorgin B relative to the metallo-center in the FtmOx1·Fe^II· αKG·1 ternary complex. The two tyrosine residues under discussion, as well as αKG and fumitremorgin B, are shown as sticks. The distance between C13 and the iron center as well as Y68 are highlighted with dashed lines, with distances labeled. D) The FtmOx1·Fe^II·αKG·1 complex structure shown in electrostatic mode (generated by APBS (Adaptive Poisson–Boltzmann Solver)), 1 is shown as orange sticks, while C13 and C26 are colored in magenta. Y68 is solvent-exposed and is shown as a sphere with green carbon and red oxygen atoms on the surface to highlight the solvent accessibility.

Scheme 1.

Key FtmOx1 catalysis information. A) Three different FtmOx1 catalysis outcomes under slightly different conditions (I–III). Verruculogen 2 could be further converted into 13-oxo-verruculogen 3 when 2 was provided as a substrate. B) Key features of the two FtmOx1 mechanistic models. In the COX-like model, Y224 is located between the Fe^IV=O and the substrate fumitremorgin B, and the Y224 radical is proposed to be responsible for the endoperoxidation and the subsequent oxidation of the substrate C13–OH to a C13 keto moiety (pathway in blue). If Y224 rotates to an alternative position, the Fe^IV=O species directly oxidizes the substrate, which leads to a hydroxylation reaction, and the proposed intermediate 21-hydroxyl-fumitremorgin B spontaneously decomposes to produce 4 (pathway in red). For the CarC-like model, it was suggested that αKG rotation is a required step.