Characterisation of a chimeric Phanerochaete chrysosporium cellobiohydrolase expressed from Escherichia coli

Abstract

The aim of this study was to purify and analyse a Phanerochaete chrysosporium cbhI.1 gene-product expressed as an inducible, secreted, heterologous protein from an Escerichia coli pGEXcbhI.1 clone. Using glutathione Sepharose 4B affinity chromatography, the expressed protein was purified from the supernatant of an induced E. coli transformed with pGEXcbhI.1 and ran as a single band on a Sodium dodecyl sulphate-polyacrylamide gel. The glutathione S-transferase (GST) fused CBHI.1 was approximately 80 kDa in size, approximately 2.2 kDa smaller than the theoretically predicted size. The purified protein exhibited time dependent hydrolytic reaction against carboxy-methyl-cellulose (CMC) and Avicel. On CMC the highest hydrolytic reaction occurred at 120 min. whereas for Avicel it was at 150 min. Optimum pH and temperature for activity of the protein against these cellulose substrates were pH 6 and 55 o C, respectively, and the protein remained stable under these optimum conditions for 24 h.