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The β glucosidase Tm bglA gene from hyperthermophile Thermotoga maritima was cloned into expression vectors pET 28a, producing two proteins of 55 kDa and 52 kDa in cell, which could be referred to Tm BglA with and without 23 amino acids. The results showed that fusion of 23 amino acids to Tm BglA improved its soluble expression and product tolerance, resulting over 60% yield of recombinant Tm BglA secreted into the growth medium in Escherichia coli JM109 (DE3). Tm BglA with 23 amino acids had higher k cat and K M values for p nitrophenyl β D glycopyranoside and much stronger product inhibition than Tm BglA without 23 amino acids. Subsequently, the Tm BglA was immobilized on chitin efficiently by genetically fusing the chitin binding domain of chitinase A1 from Thermoanaerobacterium thermosaccharolyticum DSM571. The immobilized Tm BglA had higher optimal temperature (95°C) and was more thermostable at the range from 75 to 100°C than its free form. This immobilized protein exhibited high stability and the con version yield exceeding 90%. The high level soluble expression, combined simultaneous purification and immobilization of the enzyme on chitin offers a novel approach for the low cost production of β glucosidase to produce lactose free fresh dairy products.

A thermostable uronate dehydrogenase Tb-UDH from Thermobispora bispora was over-expressed in Escherichia coli using the T7 polymerase expression system. The Tb-UDH was purified by metal affinity chromatography, and gave a single band on SDS-PAGE. The maximum activity on glucuronic acid was found at 60 °C and pH 7.0. The purified enzyme retained over 58% of its activity after holding a pH ranging from 7.0 to 7.5 for 1 h at 60 °C. The K and V values of the purified Tb-UDH for Glucuronic acid (GluUA) were 0.165 mM and 117.7 U mg, respectively, those for galacturonic acid (GalUA) were 0.115 mM and 104.2 U mg, respectively, and those for NAD were 0.120 mM and 133.3 U mg, respectively; the turnover number (k) with GluUA as a substrate was higher than that with GalUA; however, the Michaelis constant (K) for GalUA was lower than that for GluUA. After 60 min of incubation at 50 °C, Tb-UDH exhibited a conversion ratio for glucuronic acid to the glucaric acid of 84% on chemical reagent and 81.3% on hydrolysates from breech xylans formed by xylanase and α-glucuronidase. This work shows that biocatalytic routes have great potential for the conversion of hemicellulose substrate into value-added products derived from renewable biomass. TOC GRAPHIC: (A) The structure of the xylan is described and the site of action of the xylan degrading enzyme is indicated. (B) The effect of substrate concentration on recombinant Tb-UDH activity when galacturonic acid was used as substrate. (C) SDS-PAGE analysis of E. coli BL21 (DE3) harboring pET-20b(+) and pET-20b-Tb-UDH. (D) Oxidative conversion of glucuronic acid from a beechwood xylan to glucaric acid.

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