The high cost of enzymes involved in the saccharification of lignocellulosic biomass is a significant impediment to the production of biofuels from readily available biomass.  A combination of genetic and biochemical techniques led to the discovery of fungal-derived, copper-dependent polysaccharide monooxygenases (PMO), formerly known as GH61 proteins.  These hydroxylases catalyze the O2-dependent oxidative cleavage of cellulosic polysaccharides.  Different PMOs isolated from Neurospora crassa were found to generate oxidized cellodextrins modified at the reducing or non-reducing ends when aloowed to react with with cellulose and cellobiose dehydrogenase.  The non-reducing end product formed by a N. crassa PMO is a 4-keto-aldose.  Together with isotope labeling experiments, a mechanism involving oxygen insertion and subsequent elimination to break glycosidic bonds in crystalline cellulose is proposed.  Cellobiose dehydrogenase is capable of providing the reducing equivalents needed to drive the reaction.  Cellobiose dehydrogenases and proteins related to the polysaccharide monooxygenases are found throughout both ascomycete and basidiomycete fungi suggesting that this chemistry involved with oxidative cellulose degradation may be widespread throughout the fungal kingdom.

Oxidative cleavage of cellulose by fungal copper-dependent polysaccharide monooxygenases

245th National Meeting (2013)

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