19445: Investigation of GH61 proteins and their biochemical function

Degradation of lignocellulose by fungi requires the action of multiple enzymes for efficient hydrolysis of this complex, recalcitrant substrate.  In addition to the well-characterized glycoside hydrolases, there is increasing evidence that oxidative enzymes and other proteins of unknown function may facilitate degradation of plant biomass.  One family of proteins that has been shown to facilitate lignocellulose degradation through an unknown mechanism is the erroneously classified glycohydrolase 61 family. Here, quantitative proteomics was used to determine that four GH61 proteins were produced by Neurospora crassa during growth on microcrystalline cellulose and that these proteins comprise nearly 15% of the secretome by weight.  These four proteins were purified and their ability to enhance degradation of both pure cellulose and pretreated substrates was investigated.  The stimulation was both metal and oxygen dependent.  Further, the presence of another secreted protein classified as a cellobiose dehydrogenase was required for the full stimulation of activity.  These results give insight into the mechanism and specificity of GH61 action and further support the role that accessory enzymes play in degradation of recalcitrant polysaccharides.