β-Glucuronidase-coupled assays of glucuronoyl esterases

• Facile preparation of methyl esters of aromatic β-glucuronides has been introduced.
• The esters are prochromogenic substrates for microbial glucuronoyl esterases (GEs).
• The GE assays are coupled with β-glucuronidase liberating the chromophore.
• Developed spectrophotometric GE assay uses methyl ester of 4-nitrophenyl glycoside.
• A high throughput screening assay employs a glycoside leading to indigo-type dye.

Glucuronoyl esterases (GEs) are microbial enzymes with potential to cleave the ester bonds between lignin alcohols and xylan-bound 4-O-methyl-d-glucuronic acid in plant cell walls. This activity renders GEs attractive research targets for biotechnological applications. One of the factors impeding the progress in GE research is the lack of suitable substrates. In this work, we report a facile preparation of methyl esters of chromogenic 4-nitrophenyl and 5-bromo-4-chloro-3-indolyl β-D-glucuronides for qualitative and quantitative GE assay coupled with β-glucuronidase as the auxiliary enzyme. The indolyl derivative affording a blue indigo-type product is suitable for rapid and sensitive assay of GE in commercial preparations as well as for high throughput screening of microorganisms and genomic and metagenomic libraries.

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