An actinobacteria lytic polysaccharide monooxygenase acts on both cellulose and xylan to boost biomass saccharification

Abstract

Background Lytic polysaccharide monooxygenases (LPMOs) opened a new horizon for biomass deconstruction. They use a redox mechanism not yet fully understood and the range of substrates initially envisaged to be the crystalline polysaccharides is steadily expanding to non-crystalline ones. Results The enzyme Kp LPMO10A from the actinomycete Kitasatospora papulosa was cloned and overexpressed in Escherichia coli cells in the functional form with native N-terminal. The enzyme can release oxidized species from chitin (C1-type oxidation) and cellulose (C1/C4-type oxidation) similarly to other AA10 members from clade II (subclade A). Interestingly, Kp LPMO10A also cleaves isolated xylan (not complexed with cellulose, C4-type oxidation), a rare activity among LPMOs not described yet for the AA10 family. The synergistic effect of Kp LPMO10A with Celluclast ® and an endo-β-1,4-xylanase also supports this finding. The crystallographic elucidation of Kp LPMO10A at 1.6 Å resolution along with extensive structural analyses did not indicate any evident difference with other characterized AA10 LPMOs at the catalytic interface, tempting us to suggest that these enzymes might also be active on xylan or that the ability to attack both crystalline and non-crystalline substrates involves yet obscure mechanisms of substrate recognition and binding. Conclusions This work expands the spectrum of substrates recognized by AA10 family, opening a new perspective for the understanding of the synergistic effect of these enzymes with canonical glycoside hydrolases to deconstruct ligno(hemi)cellulosic biomass. Electronic supplementary material The online version of this article (10.1186/s13068-019-1449-0) contains supplementary material, which is available to authorized users.

Four cellulose-active lytic polysaccharide monooxygenases from Cellulomonas species

“…To our knowledge, this pattern has not been previously reported. Possible exceptions are Tt LPMO10A, which contains a Tyr but was reported to have mixed C1/C4 activity [ 73 ], and Kp LPMO10A, which has a Trp and was reported to have both mixed regioselectivity and activity on both cellulose and chitin [ 107 ]. In addition, a similar trend was observed concerning the axial aromatic residue at the active site (Phe or Tyr) [ 103 , 108 ].…”

“…We observed that whereas C1-active AA10 LPMOs contain an axial Phe (regardless of cellulose or chitin specificity), mixed C1/C4-active AA10 LPMOs possess a Tyr at this position. Again, the only exceptions to this pattern among characterized AA10 members are Tt LPMO10A and Kp LPMO10A [ 73 , 107 ].…”

Current understanding of substrate specificity and regioselectivity of LPMOs

“…They are C1/ C4-specific for cellulose oxidation and C1-specific for chitin oxidation. Recently, a multifunctional LPMO10, KpLPMO10A has been reported that besides chitin-and cellulose-activity, it can also act on xylan to produce C4-oxidized products (Correa et al 2019). In addition, it is reported that, PaLPMO9H is C4-specific on mixedlinkage glucans, and C1/C4-specific on glucomannan (Fanuel et al 2017).…”

Biochemical, structural insights of newly isolated AA16 family of Lytic Polysaccharide Monooxygenase (LPMO) fromAspergillus fumigatusand investigation of its synergistic effect using biomass

“…The LPMOs are important for their auxiliary activity. It enhances the activity of Cellulase enzyme for degradation of cellulose and lignocelluloses (Corrêa et al 2019). The only identified AA16 family, the AaAA16 showed sequential synergistic effect with T. reesei CBHI on nano-fibrillated cellulose (NFC) and PASC.…”