1 Department of Chemistry and Bioscience, The Faculty of Engineering and Science, Aalborg University, VBN2 Section for Sustainable Biotechnology, Copenhagen, The Faculty of Engineering and Science, Aalborg University, VBN3 The Faculty of Engineering and Science, Aalborg University, VBN4 Aalborg University Copenhagen, The Faculty of Humanities, Aalborg University, VBN5 Chengdu Institute of Biology, Chinese Academy of Sciences
Mucor circinelloides produces plant cell wall degrading enzymes that allow it to grow on complex polysaccharides. Although the genome of M. circinelloides has been sequenced, only few plant cell wall degrading enzymes are annotated in this species. We applied peptide pattern recognition, which is a non-alignment based method for sequence analysis to map conserved sequences in glycoside hydrolase families. The conserved sequences were used to identify similar genes in the M. circinelloides genome. We found 12 different novel genes encoding members of the GH3, GH5, GH9, GH16, GH38, GH47 and GH125 families in M. circinelloides. One of the two GH3-encoding genes was predicted to encode a β-glucosidase (EC 220.127.116.11). We expressed this gene in Pichia pastoris KM71H and found that the purified recombinant protein had relative high β-glucosidase activity (1.73U/mg) at pH5 and 50°C. The Km and Vmax with p-nitrophenyl-β-d-glucopyranoside as substrate was 0.20mM and 2.41U/mg, respectively. The enzyme was not inhibited by glucose and retained 84% activity at glucose concentrations up to 140mM. Although zygomycetes are not considered to be important degraders of lignocellulosic biomass in nature, the present finding of an active β-glucosidase in M. circinelloides demonstrates that enzymes from this group of fungi have a potential for cellulose degradation.
Enzyme and Microbial Technology, 2014, Vol 67, p. 47-52