A paper published in the recent issue of PNAS “Insights into the oxidative degradation of cellulose by a copper metalloenzyme that exploits biomass components” by Quinlan et al. succeeds in characterizing an important aspect of the breakdown of cellulose by enzymes. I’m interested in the use of cellulose in bioenergy purposes, but one of the major problems in its use is extreme recalcitrance of the polysaccaride. By fully understanding the enzymatic mechanisms of the breakdown of cellulose we can surpass a major scientific and economic challenge for the effective release of bioenergy from biomass.
Cellulose is typically broken down by fungi employing a suite of different enzymes. These enzymes are traditionally placed into two classes: endoglucanases and cellobiohydrolases. In this paper, the authors identify the enzymatic abilities of a newly recognized enzyme class, called the GH61 glycoside hydrolases (see Harris et al. for more information on GH61 glycoside hydrolases). The GH61 glycoside hydrolases greatly increase the efficiency of the endoglucanases and cellobiohydrolases and recent genome sequencing of brown rot fungi, such as Postia placenta, show numerous GH61 glycoside hydrolases.
The authors describe the 3D structure of a GH61 glycoside hydrolase from Thermoascus aurantiacus identifying the active site details and catalytic activity of the enzyme. It was identified that the GH61 glycoside hydrolase enzymes are oxidizing agents and the authors show the direct degradation of cellulose. Furthermore, the authors identify copper as the metal cofactor of the enzyme and show a unique methyl modification of a metal-coordinating histidine residue.
See here for commentary on the paper.