Biochemical Characterization and Synergistic Assessment of Thermophilic Glycoside Hydrolases for Hemicellulose Depolymerization

Abstract

Consolidated Bioprocessing (CBP) represents a promising platform for lignocellulosic biofuel production, yet its kinetic efficiency is fundamentally constrained by the structural recalcitrance of highly branched hemicellulose networks. To overcome these depolymerization bottlenecks, this study investigates the biochemical boundaries and cooperative dynamics of novel cellulosomal glycoside hydrolases derived from the thermophilic bacterium Acetivibrio thermocellus. Specifically, three distinct multi-modular architectures were selected for functional characterization: Clo1313 2857 (a GH43 10 α-L-arabinofuranosidase), Clo1313 2216 (a GH43 4 endo-α-1,5-L-arabinanase), and Clo1313 2795 (a multidomain GH30/GH43 20 construct). Recombinant targets were successfully expressed in Escherichia coli and isolated via immobilized metal affinity chromatography. Extensive profiling established isolated operating windows, with the GH43 catalytic cores exhibiting robust thermophilic activity between 60 ◦C and 70 ◦C at mildly acidic to neutral pH (5.0–7.0). Substrate specificity and depolymerization modalities were subsequently validated through colorimetric reducing-sugar assays and High-Performance Liquid Chromatography (HPLC). Clo1313 2857 demonstrated strict exo-debranching activity on wheat arabinoxylan (WAX), yielding exclusive L-arabinose monomers. Clo1313 2216 exhibited targeted endo-acting cleavage on sugar beet arabinan (SBA), accumulating higher-order oligosaccharide intermediates and displaying a pronounced non-linear kinetic lag phase at low enzyme concentrations (<0.015 μM). Building upon these isolated kinetic parameters, the cooperative dynamics of the hemicellulases were evaluated through systematic combinatorial screening. Combinatorial assays on SBA identified a highly active synergistic pairing between the endo-arabinanase Clo1313 2216 and the exo-acting AtAbf43C (Clo1313 2794), yielding a 1.91-fold increase in specific activity (U/mg). Further stoichiometric validation via the method of continuous variation defined a mathematically optimal 2 μmol Clo1313 2216: 3 μmol AtAbf43C formulation. Kinetic analysis confirmed that this synergy is driven by mechanistic compensation. The exo-enzyme cleaves the oligosaccharides generated by the endo-enzyme, alleviating the non-productive lag phase and yielding a 15-fold recovery in specific activity at low concentrations of Clo1313 2216. Ultimately, the precise biochemical characterization of these domains, coupled with empirical evidence of stoichiometric synergism, provides a foundation for engineering architectures necessary for robust monomer release during CBP fermentation.