Tammy Hsu

Title

Protecting Groups for Improved Control of Indigo Biosynthesis

Authors

Tammy M. Hsu, Zachary N. Russ, John E. Dueber

Abstract

Indigo is a widely used dye in the textile industry, but the water insolubility of the indigo
molecule makes the dyeing process challenging. The current industry standard uses toxic reducing agents to reduce indigo to leucoindigo, a soluble but unstable intermediate. We are developing a more environmentally friendly, biomimetic process to produce indigo in E. coli. In the leaves of indigo plants such as Polygonum tinctorium, indole is oxidized to indoxyl and immediately glucosylated to make stable, soluble indican. When the leaf tissue is damaged, a β- glucosidase can hydrolyze indican back to indoxyl, which dimerizes into indigo in the presence of oxygen.
Looking to the indigo plant for inspiration, we have engineered E. coli to protect indoxyl in its monomeric form by glucosylation. We purified and identified the native indoxyl glucosyltransferase from P. tinctorium, and we have used it to protect biosynthesized indoxyl in vivo. The resulting indican can be exported from the cell and used for dyeing applications. The addition of β-glucosidase can â??deprotectâ? indican, forming indigo. The strategy of biological protecting groups could also be used to make other reactive products of interest more tractable.