L2 loop engineering enhances the enzymatic activity and synergism property of the AA16 family Lytic polysaccharide monooxygenase enzyme from Aspergillus fumigatus

Lytic polysaccharide monooxygenase (LPMO) is an enzyme that has enormous potential for industrial applications. It has a synergistic effect with the cellulase enzyme complex. The LPMO enzymes typically adopt a compact β-sandwich fold that consists of a 7 to 9 β-strand with a flat active site containing copper in its active site. There are a few loops in LPMO, among them the L2 loop is reported to take a key role in shaping the active site and substrate binding. Now, in this work, we want to investigate the role of the L2 loop in enzymatic activity and synergistic effect. In achieving our goal, we have replaced the L2 loop of our concerning Af LPMO16 with other L2 loops from different LPMOs: Hi LPMO9B (PDB: 5NNS), Mc LPMO9 (PDB: 7NTL) and Cs LPMO9 (PDB: 7EXK). Interestingly, L2 loop replacement from Cs LPMO9 (PDB: 7EXK) showed enhanced activity and synergism compared to others. The secondary structural analysis by circular dichroism also suggested that it changed the structure significantly. Moreover, this is the first report of complete L2 loop engineering in LPMO.