GH10 xylanase D from Penicillium funiculosum: biochemical studies and xylooligosaccharide production

Background: The filamentous fungus Penicillium funiculosum produces a range of glycoside hydrolases (GH). The XynD gene, encoding the sole P. funiculosum GH10 xylanase described so far, was cloned into the pPICZ alpha A vector and expressed in methylotrophe yeast Pichia pastoris, in order to compare the results obtained with the P. funiculosum GH11 xylanases data. Results: High level expression of recombinant XynD was obtained with a secretion of around 60 mg.L-1. The protein was purified to homogeneity using one purification step. The apparent size on SDS-PAGE was around 64 kDa and was 46 kDa by mass spectrometry thus higher than the expected molecular mass of 41 kDa. The recombinant protein was N- and O-glycosylated, as demonstrated using glycoprotein staining and deglycosylation reactions, which explained the discrepancy in molecular mass. Enzyme-catalysed hydrolysis of low viscosity arabinoxylan (LVAX) was maximal at pH 5.0 with Km((app)) and k(cat)/ Km((app)) of 3.7 +/- 0.2 (mg.mL(-1)) and 132 (s(-1)mg(-1).mL), respectively. The activity of XynD was optimal at 80 C and the recombinant enzyme has shown an interesting high thermal stability at 70 C for at least 180 min without loss of activity. The enzyme had an endo-mode of action on xylan forming mainly xylobiose and short-chain xylooligosaccharides (XOS). The initial rate data from the hydrolysis of short XOS indicated that the catalytic efficiency increased slightly with increasing their chain length with a small difference of the XynD catalytic efficiency against the different XOS. Conclusion: Because of its attractive properties XynD might be considered for biotechnological applications. Moreover, XOS hydrolysis suggested that XynD possess four catalytic subsites with a high energy of interaction with the substrate and a fifth subsite with a small energy of interaction, according to the GH10 xylanase literature data.