Structural and functional insights of beta-glucosidases identified from the genome of Aspergillus fumigatus

摘要

Thermostable glucose tolerant beta-glucosidase from Aspergillus species has attracted worldwide interest for their potentiality in industrial applications and bioethanol production. A strain of Aspergillus fumigatus (AfNITDGPICA3) identified by our laboratory from straw retting ground showed higher cellulase activity, specifically the beta-glucosidase activity, compared to other contemporary strains. Though A. fumigatus has been known for high cellulase activity, detailed identification and characterization of the cellulase genes from their genome is yet to be done. In this work we have been analyzed the cellulase genes from the genome sequence database of Aspergillus fumigatus (Af293). Genome analysis suggests two cellobiohydrolase, eleven endoglucanase and seventeen beta-glucosidase genes present. beta-Glucosidase genes belong to either Glycohydro1 (GH1 or Bgl1) or Glycohydro3 (GH3 or Bgl3) family. The sequence similarity suggests that Bgl1 and Bgl3 of A. fumagatus are phylogenetically close to those of A. fisheri and A. oryzae. The modelled structure of the Bgl1 predicts the (beta/alpha)(8) barrel type structure with deep and narrow active site, whereas, Bgl3 shows the (alpha/beta)(8) barrel and (alpha/beta)(6) sandwich structure with shallow and open active site. Docking results suggest that amino acids Glu544, Glu466, Trp408,Trp567,Tyr44,-Tyr222,Tyr770,Asp844,Asp537,Asn212,Asn217 of Bgl3 and Asp224,Asn242,Glu440, Glu445, Tyr367, Tyr365,Thr994,Trp435,Trp446 of Bgl1 are involved in the hydrolysis. Binding affinity analyses suggest that Bgl3 and Bgl1 enzymes are more active on the substrates like 4-methylumbelliferyl glycoside (MUG) and p-nitrophenyl-beta-D-1, 4-glucopyranoside (pNPG) than on cellobiose. Further docking with glucose suggests that Bgl1 is more glucose tolerant than Bgl3. Analysis of the Aspergillus fumigatus genome may help to identify a beta-glucosidase enzyme with better property and the structural information may help to develop an engineered re