Insights into the oxidative degradation of cellulose by a copper metalloenzyme that exploits biomass componentsR. Jason Quinlan, Matt Sweeney, Leila Lo Leggio et al.|Proceedings of the National Academy of Sciences|2011 The enzymatic degradation of recalcitrant plant biomass is one of the key industrial challenges of the 21st century. Accordingly, there is a continuing drive to discover new routes to promote polysaccharide degradation. Perhaps the most promising approach involves the application of "cellulase-enhancing factors," such as those from the glycoside hydrolase (CAZy) GH61 family. Here we show that GH61 enzymes are a unique family of copper-dependent oxidases. We demonstrate that copper is needed for GH61 maximal activity and that the formation of cellodextrin and oxidized cellodextrin products by GH61 is enhanced in the presence of small molecule redox-active cofactors such as ascorbate and gallate. By using electron paramagnetic resonance spectroscopy and single-crystal X-ray diffraction, the active site of GH61 is revealed to contain a type II copper and, uniquely, a methylated histidine in the copper's coordination sphere, thus providing an innovative paradigm in bioinorganic enzymatic catalysis.
Sabatier Principle for Interfacial (Heterogeneous) Enzyme CatalysisThe Sabatier principle states that optimal catalysis occurs when interactions between catalyst and substrate are of intermediary strength. Although qualitative in nature, this concept has proven extremely useful within (nonbiochemical) heterogeneous catalysis. In the current work, we show that the principle may be applied to an interfacial enzyme reaction. Specifically, we studied the breakdown of cellulose by different cellulases (wild types and variants) and found that the results could be rationalized in so-called volcano plots that are emblematic of the principle. This implies that the rate of the complex enzymatic reaction can be described by a single parameter (binding strength), and we show how this may help elucidating e.g. rate-controlling steps and relationships of substrate load and enzymatic efficacy. On a more general level, we propose that the Sabatier principle may be widely applicable to interfacial enzyme processes and hence open an avenue to the application within biocatalysis of some of the principles and practices originally developed for heterogeneous catalysis.