Multilevel metabolic and enzyme engineering enables efficient biosynthesis of cyanidin-3-O-glucoside from dihydroquercetin in Escherichia coli.

Abstract

Cyanidin-3-O-glucoside (C3G) is a water-soluble, value-added natural flavonoid with extensive applications in the nutraceutical and cosmetic industries. However, its efficient bioproduction is hampered by intermediate instability, metabolic imbalance and enzyme kinetic constraints. Here, we successfully constructed an efficient biosynthesis pathway from the dihydroquercetin (DHQ) to C3G in Escherichia coli through a multilevel engineering strategy. Initially, the integration of glutathione S-transferase (GST) redirected the metabolic flux towards target cyanidin formation. To minimize the dissipation of labile intermediates, pathway enzymes were spatially organized within a protein cage to enhance cascade efficiency. Furthermore, genomic integration of Glycine max sucrose synthase established an in-situ UDP-glucose regeneration module to ensure a continuous precursor supply for the final glycosylation step. After these pathway-level optimizations, the key enzyme dihydroflavonol 4-reductase (FaDFR) emerged as a new rate-limiting bottleneck due to substrate inhibition under increased DHQ loading. Structure-guided and evolution-informed engineering generated FaDFR variants with improved high-substrate tolerance, as supported by in vitro activity profiling and molecular dynamics simulations. Through combined pathway and enzyme engineering, the G130C-containing strain achieved a C3G titer of 1.34 g/L, representing a 23-fold improvement over the GST-assisted baseline strain. Our platform enables efficient, value-added C3G production and provides a promising framework for constructing downstream pathways toward structurally diverse anthocyanin derivatives.