Heterologous expression and characterization of novel GH12 β-glucanase and AA10 lytic polysaccharide monooxygenase from Streptomyces megaspores and their synergistic action in cellulose saccharification.

Background: The combination of cellulase and lytic polysaccharide monooxygenase (LPMO) is known to boost enzymatic saccharification of cellulose. Although the synergy between cellulases (GH5, 6 or 7) and LPMOs (AA9) has been extensively studied, the interplay between other glycoside hydrolase and LPMO families remains poorly understood.

Results: In this study, two cellulolytic enzyme-encoding genes SmBglu12A and SmLpmo10A from Streptomyces megaspores were identified and heterologously expressed in Escherichia coli. The recombinant SmBglu12A is a non-typical endo-β-1,4-glucanase that preferentially hydrolyzed β-1,3-1,4-glucans and slightly hydrolyzed β-1,4-glucans and belongs to GH12 family. The recombinant SmLpmo10A belongs to a C1-oxidizing cellulose-active LPMO that catalyzed the oxidation of phosphoric acid swollen cellulose to produce celloaldonic acids. Moreover, individual SmBglu12A and SmLpmo10A were both active on barley β-1,3-1,4-glucan, lichenan, sodium carboxymethyl cellulose, phosphoric acid swollen cellulose, as well as Avicel. Furthermore, the combination of SmBglu12A and SmLpmo10A enhanced enzymatic saccharification of phosphoric acid swollen cellulose by improving the native and oxidized cello-oligosaccharides yields.

Conclusions: These results proved for the first time that the AA10 LPMO was able to boost the catalytic efficiency of GH12 glycoside hydrolases on cellulosic substrates, providing another novel combination of glycoside hydrolase and LPMO for cellulose enzymatic saccharification.