On the roles of auxiliary proteins and enzymes in cellulose surface degradation: swollenin and lytic polysaccharide monooxygenase

Ever since Elwyn T. Reese's C1-Cx postulate, that invokes a nonhydrolytic, cellulose structure-disrupting C1 factor assisting in the conversion of cellulosic substrates by hydrolytic enzymes (the Cx factor), the discovery of proteins and enzymes potentially playing a C1-like functional role has attracted much attention. Expansin-like proteins appear to lack enzyme activity but adsorb to cellulose. Due to physical interactions with the cellulose surface, expansin-like proteins are thought to induce structural changes in the substrate, often referred to as "amorphogenesis". It is through the amorphogenesis effect that expansin-like proteins are believed to facilitate enzymatic hydrolysis by cellulases. A number of recent reports indicate synergy between expansin-like proteins and hydrolytic enzymes in cellulose degradation. We present results of a study on swollenin SWO1 (a major expansin-like protein) from the fungus Hypocrea jecorina. SWO1 was obtained through overexpression in the native host and its binding to cellulose, hemicellulose and lignin was characterized. Using atomic force microscopy (AFM) in liquid environment, consequences of "action" of swollenin of the surface of different celluloses was analyzed.

Another candidate C1 factor is the lytic polysaccharide monooxygenase (LPMO). The LPMO presents a new paradigm of oxidative O₂-dependent polysaccharide cleavage and its action of the cellulose surface was recently shown to affect positively the surface-bound activity of cellulases. Using AFM we analyzed in real time dynamic features of the interaction of LPMO (from Neurospora crassa) with the surface of a crystalline cellulose substrate.