Liquid Phase Multiplex High-Throughput Screening of Metagenomic Libraries Using p-Nitrophenyl-Linked Substrates for Accessory Lignocellulosic Enzymes

Characterisation of three novel α-L-arabinofuranosidases from a compost metagenome

BACKGROUND

The importance of the accessory enzymes such as α-L-arabinofuranosidases (AFases) in synergistic interactions within cellulolytic mixtures has introduced a paradigm shift in the search for hydrolytic enzymes. The aim of this study was to characterize novel AFase genes encoding enzymes with differing temperature optima and thermostabilities for use in hydrolytic cocktails.

RESULTS

Three fosmids, pFos-H4, E3 and D3 were selected from the cloned metagenome of high temperature compost, expressed in Escherichia coli and subsequently purified to homogeneity from cell lysate. All the AFases were clustered within the GH51 AFase family and shared a homo-hexameric structure. Both AFase-E3 and H4 showed optimal activity at 60 °C while AFase-D3 had unique properties as it showed optimal activity at 25 °C as well as the ability to maintain substantial activity at temperatures as high as 90 °C. However, AFase-E3 was the most thermostable amongst the three AFases showing full activity even at 70 °C. The maximum activity was observed at a pH profile between pH 4.0-6.0 for all three AFases with optimal activity for AFase H4, D3 and E3 at pH 5.0, 4.5 and 4.0, respectively. All the AFases showed K_M range between 0.31 mM and 0.43 mM, K_cat range between 131 s^- 1 and 219 s^- 1 and the specific activity for AFase-H4, AFases-E3 and was 143, 228 and 175 U/mg, respectively. AFases-E3 and D3 displayed activities against pNP-β-L-arabinopyranoside and pNP-β-L-mannopyranoside respectively, and both hydrolysed pNP-β-D-glucopyranoside.

CONCLUSION

All three AFases displayed different biochemical characteristics despite all showing conserved overall structural similarity with typical domains of AFases belonging to GH51 family. The hydrolysis of cellobiose by a GH51 family AFase is demonstrated for the first time in this study.

Carbohydrate active enzyme domains from extreme thermophiles: components of a modular toolbox for lignocellulose degradation

Lignocellulosic biomass is a promising feedstock for the manufacture of biodegradable and renewable bioproducts. However, the complex lignocellulosic polymeric structure of woody tissue is difficult to access without extensive industrial pre-treatment. Enzyme processing of partly depolymerised biomass is an established technology, and there is evidence that high temperature (extremely thermophilic) lignocellulose degrading enzymes [carbohydrate active enzymes (CAZymes)] may enhance processing efficiency. However, wild-type thermophilic CAZymes will not necessarily be functionally optimal under industrial pre-treatment conditions. With recent advances in synthetic biology, it is now potentially possible to build CAZyme constructs from individual protein domains, tailored to the conditions of specific industrial processes. In this review, we identify a 'toolbox' of thermostable CAZyme domains from extremely thermophilic organisms and highlight recent advances in CAZyme engineering which will allow for the rational design of CAZymes tailored to specific aspects of lignocellulose digestion.