Question

Write the stages of isolation and purification of Beta-Glucuronidase from the sources, and the protocol you will put forward will aim to have the highest and purest enzyme structure. Basic protein separation and purification methods and techniques will be used in the preparation of this protocol.

Answer 1

Beta-glucuronidase from Pectinex Ultra SP-L, a commercial pectolytic enzyme preparation from Aspergillus niger, was purified 170-fold by ion-exchange chromatography and gel filtration. Apparent M(r) of the purified enzyme, estimated by denaturing gel electrophoresis and size-exclusion chromatography, were 68,000 and 71,000, respectively, indicating that the enzyme is a monomeric protein. It released uronic acids not only from p-nitrophenyl beta-glucosiduronic acid (PNP-GlcA) but also from acidic galactooligosaccharides carrying either beta-D-glucosyluronic or 4-O-methyl-beta-D-glucosyluronic residues at the nonreducing termini through beta-(1-->6)-glycosidic linkages. The enzyme exhibited a maximal activity toward these substrates at pH 3.0. A regioisomer, 3-O-beta-glucosyluronic acid-galactose, was unsusceptible to the enzyme. The enzyme did act on a polymer substrate, releasing uronic acid from the carbohydrate portion of a radish arabinogalactan-protein modified by treatment with fungal alpha-L-arabinofuranosidase. The enzyme produced acidic oligosaccharides by transglycosylation, catalyzing the transfer of uronic acid residues of PNP-GlcA and 6-O-beta-glucosyluronic acid-galactose to certain exogenous acceptor sugars such as Gal, N-acetylgalactosamine, Glc, and xylose

  The enzyme with GUS activity was partially purified from a crude protein extract of Arabidopsis stem tissue. Enzyme activity was monitored with p-nitrophenyl-β-D-glucuronide (pNPGlcA) as a substrate and tested in acidic conditions. The purification protocol involved three column chromatography steps: lectin concanavalin A (ConA) chromatography, cation-exchange chromatography and gel filtration. A single peak of GUS activity was eluted from the lectin ConA Sepharose column. The corresponding fractions were then subjected to cation-exchange chromatography on a CM-Sepharose column. One peak of activity corresponding to proteins eluted with 250 mM NaCl was detected. To increase specific GUS activity, the corresponding fractions were subjected to a final purification step (exclusion chromatography on Superdex 200) and a single peak of activity was eluted. Based on the elution of known markers, this peak corresponds to proteins of ∼55 kDa.An optimum pH of 5.0 and temperature of 55°C were determined for this partially purified enzyme .This final extract exhibited no activity above the background when p-nitrophenyl-α-D-glucuronide was used as a substrate (data not shown), indicating a specificity of the partially purified enzyme for beta-linked glucuronosyl residues.