Characterization of a Protease-Resistant Endotype-Cellulase from the Basidiomycete Irpex lacteus.

Abstract

The endo-type cellulase (En-1) from the basidiomycete Irpex lacteus was found to be highly resistant to proteases and nonionic surfactants. En-1 showed no loss of activity when incubated with proteases such as V8 protease, papain, trypsin, proteinase K and various nonionic surfactants at pH 7.5 for at least 3 days. To investigate the effect of the carbohydrate chain of En-1 on its resistance to proteolysis, carbohydrate-depleted enzymes were prepared. The native and carbohydrate-depleted enzymes showed the same resistance to protease digestion, suggesting that the carbohydrate chain of En-1 does not contribute to the resistance to proteolysis. On the other hand, with a shift of pH from 7.5 to 8.0 or 8.5, the resistance to protease digestion was decreased. Comparison of the circular dichroism (CD) spectra at pH 7.5, pH 8.0, and pH 8.5 suggested that the resistance to proteolysis depended on the change in the structure of En-1. The N-terminal amino acid sequence of En-1 showed considerable homology to N-terminal sequences of endo-β-1, 4-glucanases from other fungi, namely, Schizophyllum commune, Sclerotinia sclerotiorum, Aspergillus niger, and Macrophomina phaseolina.