Enzymatic synthesis of indigo derivatives by tuning P450 BM3 peroxygenases

Abstract

Indigoids, a class of bis-indoles, have long been applied in dyeing, food, and pharmaceutical industries. Recently, interest in these 'old' molecules has been renewed in the field of organic semiconductors as functional building blocks for organic electronics due to their excellent chemical and physical properties. However, these indigo derivatives are difficult to access through chemical synthesis. In this study, we engineer cytochrome P450 BM3 from an NADPH-dependent monooxygenase to peroxygenases through directed evolution. A select number of P450 BM3 variants are used for the selective oxidation of indole derivatives to form different indigoid pigments with a spectrum of colors. Among the prepared indigoid organic photocatalysts, a majority of indigoids demonstrate a reduced band gap than indigo due to the increased light capture and improved charge separation, making them promising candidates for the development of new organic electronic devices. Thus, we present a useful enzymatic approach with broad substrate scope and cost-effectiveness by using low-cost H₂O₂ as a cofactor for the preparation of diversified indigoids, offering versatility in designing and manufacturing new dyestuff and electronic/sensor components.

Keywords: Cytochrome P450 enzymes; Dyestuff; Indigoids; Organic electronics; P450 BM3 peroxygenase.

Graphical abstract

Fig. 1

The selected mutational sites of P450 BM3* (PDB ID code: 2X80). The key amino acids grouped into six sites are shown as sticks with different colors.

Fig. 2

Dimerization of various indole derivates by P450 BM3^T1. Each product is a mixture of indigo-like and indirubin-like derivatives.

Fig. 3

The structures and colors of the indigoids produced by P450 BM3^T1. RGB values of the prepared dyes are obtained using the Photoshop's Color Picker.

Fig. 4

Photocurrents and bandgap values for indigoids of the Tauc plot.