Oxidative cleavage of some cellulosic substrates by auxiliary activity (AA) family 9 enzymes influences the adsorption/desorption of hydrolytic cellulase enzymes

Abstract

Auxiliary Activity family 9 (AA9) enzymes (lytic polysaccharide monooxygenase) have been shown to significantly boost the hydrolytic efficiency of canonical cellulase enzymes through the oxidative cleavage/disruption of the highly recalcitrant crystalline cellulose region. In the work reported here, although the addition of AA9 to a commercial cellulase mixture decreased the extent of cellulase enzyme adsorption during hydrolysis of some cellulosic substrates, such as avicel, dissolving pulp (DSP) and steam pretreated biomass, it had little or no effect on others (cellulose nanocrystalline (CNC), phosphoric acid swollen cellulose (PASC), and cellulose II/cellulose III cellulosic substrates). When specific cellulase enzyme adsorption/desorption profiles were determined during cellulose hydrolysis, using a double-antibody sandwich enzyme linked immunosorbent assay (ELISA), the AA9 enzyme was found to increase desorption of Cel7A (a processive exoglucanase), but not Cel7B (an endoglucanase). The increase in the amount of acid groups on the residual substrates (measured using conductometric titration) resulting from the action of AA9, was a likely reason for the observed reduction in Cel7A adsorption. The residual acid group content also indicated that only a certain amount of surface crystalline cellulose (assessed by the cellulose binding module (CBM) technique) was attacked by AA9. Although the vast majority of the AA9 remained in the supernatant during hydrolysis of most of the cellulosic substrates its adsorption to the residual steam pretreated lodgepole pine was likely due to the affinity of the AA9 to softwood lignin.