Enzymology
High-resolution structure of a lytic polysaccharide monooxygenase from Hypocrea jecorina reveals a predicted linker as an integral part of the catalytic domain
For decades, the enzymes of the fungus Hypocrea jecorina have served as a model system for the breakdown of cellulose. Three-dimensional structures for almost all H. jecorina cellulose-degrading enzymes are available, except for HjLPMO9A, belonging to the AA9 family of lytic polysaccharide monooxygenases (LPMOs). These enzymes enhance the hydrolytic activity of cellulases and are essential for cost-efficient conversion of lignocellulosic biomass. Here, using structural and spectroscopic analyses, we found that native HjLPMO9A contains a catalytic domain and a family-1 carbohydrate-binding module (CBM1) connected via a linker sequence.Temperature Effects on Kinetic Parameters and Substrate Affinity of Cel7A Cellobiohydrolases
Background: Temperature concomitantly modulates kinetic and adsorption properties in heterogeneous enzyme catalysis.Results: Affinity-activity relationships for four Cel7A cellobiohydrolases are characterized over a broad temperature interval.Conclusion: Cellobiohydrolases are strongly activated by temperature at high, but not at low, substrate loads.Significance: Fundamental insight into cellulolytic mechanisms at high (industrially relevant) temperatures is gained.Free Energy Diagram for the Heterogeneous Enzymatic Hydrolysis of Glycosidic Bonds in Cellulose
Background: Heterogeneous enzyme catalysis is common but has rarely been rationalized through free energy diagrams.Results: The thermodynamic properties of stable and activated cellulase complexes are reported.Conclusion: The rate of enzyme-substrate complexation is entropy-controlled, whereas dissociation is controlled by enthalpy.Significance: Supposedly, this is the first elucidation of the transition states for the complexation and dissociation steps of a cellulase.
