Biosynthesis of Rhamnosylated Anthraquinones in Escherichia coli

Rhamnose is a naturally occurring deoxysugar present as a glycogenic component of plant and microbial natural products. A recombinant mutant Escherichia coli strain was developed by overexpressing genes involved in the TDP-(L)-rhamnose biosynthesis pathway of different bacterial strains and Saccharothrix espanaensis rhamnosyl transferase to conjugate intrinsic cytosolic TDP-(L)-rhamnose with anthraquinones supplemented exogenously. Among the five anthraquinones (alizarin, emodin, chrysazin, anthrarufin, and quinizarin) tested, quinizarin was biotransformed into a rhamoside derivative with the highest conversion ratio by whole cells of engineered E. coli. The quinizarin glycoside was identified by various chromatographic and spectroscopic analyses. The anti-proliferative property of the newly synthesized rhamnoside, quinizarin-4-O-α-(L)-rhamnoside, was assayed in various cancer cells.