Joint X-ray crystallographic and characterization study of the endoglucanase Cel45A from Phanerochaete chrysosporium, a glycoside hydrolase (GH) family 45 member

The basidiomycete fungus Phanerochaette chrysosporium produces multienzymes able to efficiently hydrolyze cellulose fibers. These enzymes, called cellulases have been the subject of an intense interest due to their ability to convert the cellulosic biomass into soluble sugars. The cellulose is the most abundant biopolymer in the planet, thus the ethanol produced from plant biomass  is one attractive option of biofuel nowadays. Too little is known about cellulases produced by P. chrysosporium especially regarding enzymes belonging to the GH family 45. Here we report the structure of the endoglucanase Cel45A from P. chrysosporium, a GH family 45 member. The crystallographic structure was refined at 1.4 Å resolution and reveal some similarities between Cel45A and two other representatives within this family (maEG and EGV). An interesting feature observed is a six-stranded β-barril domain. The overall shape of Cel45A is a flattened sphere and the structure of the β-barril is connected with a disulfide-bonded loop. Moreover, a long open groove is present in the surface of the protein, which is related to the catalytic activity. Furthermore, we characterized the recombinant protein and demonstrate its synergism with a cellobiohydrolase (CBHI). We have also verified that this enzyme has a considerable thermal stability, which might be interesting for industrial applications.