Lytic polysaccharide monooxygenases disrupt the cellulose fibers structure

Abstract

Lytic polysaccharide monooxygenases (LPMOs) are a class of powerful oxidative enzymes that breakdown recalcitrant polysaccharides such as cellulose. Here we investigate the action of LPMOs on cellulose fibers. After enzymatic treatment and dispersion, LPMO-treated fibers show intense fibrillation. Cellulose structure modifications visualized at different scales indicate that LPMO creates nicking points that trigger the disintegration of the cellulose fibrillar structure with rupture of chains and release of elementary nanofibrils. Investigation of LPMO action using solid-state NMR provides direct evidence of modification of accessible and inaccessible surfaces surrounding the crystalline core of the fibrils. The chains breakage likely induces modifications of the cellulose network and weakens fibers cohesion promoting their disruption. Besides the formation of new initiation sites for conventional cellulases, this work provides the first evidence of the direct oxidative action of LPMOs with the mechanical weakening of the cellulose ultrastructure. LPMOs can be viewed as promising biocatalysts for enzymatic modification or degradation of cellulose fibers.

Single-molecule study of oxidative enzymatic deconstruction of cellulose

“…Computational studies support the intuition 18 , but experimental evidence on the presumed deconstruction effect of LPMO action is lacking. Very recently 19 , solid-state NMR studies combined with AFM microscopy showed micron-sized cellulose fibers from bleached softwood to become globally disrupted upon incubation with LPMO. Here we were able to visualize local fibrillation events, which are occurring at the side walls of the cellulose nanocrystals, in consequence of treatment with LPMO.…”

“…LPMO structures suggest a likely binding mode of the enzyme to cellulose surfaces via the protein face that exposes the catalytic metal outward 9 . Oxidative chain cleavages in crystalline areas of the substrate are expected to cause local disruptions of the ordered cellulose structure 18, 19 . This decrystallization of the substrate might facilitate the hydrolytic chain depolymerization by cellulases.…”

Oxygen Activation by Cu LPMOs in Recalcitrant Carbohydrate Polysaccharide Conversion to Monomer Sugars

“…Researchers have turned to atomic force microscopy, solid state NMR, high-performance size exclusion chromatography coupled with light scattering and refractive index detection (Villares et al), and confocal microscopy (Eibinger et al) to directly measure changes to cellulose fibers after treatment with Podospora anserina LPMO9H ( Pa LPMO9H). 178,179 …”

Structural and molecular dynamics studies of a C1‐oxidizing lytic polysaccharide monooxygenase from Heterobasidion irregulare reveal amino acids important for substrate recognition

“…However, the exact role and mechanism by which LPMOs aid in lignocellulosic biomass deconstruction remains largely unknown. Many fungal AA9 LPMOs appear to release oxidized glucans from crystalline cellulose substrates , but it has also been suggested, through the application of advanced microscopy techniques, that some AA9 LPMOs could either disrupt the morphological structure of cellulose nanofibers or introduce oxidative cleavages on the crystalline region of the cellulose surface . Additionally, AA9 LPMOs act synergistically with glycoside hydrolases to decompose cellulose to glucose monomers .…”