Abstract
Auxiliary activity family 9 (AA9, formerly known as glycoside hydrolase family 61 or polysaccharide monooxygenase) is a group of fungal proteins that were recently found to have a significant synergism with cellulase in cellulose hydrolysis via the oxidative cleavage of glycosidic bonds of cellulose chains. In this study, we report the active expression of a recombinant fungal AA9 from Chaetomium globosum (CgAA9) in a bacterial host, Escherichia coli, and the optimization of its synergistic activity in cellulose hydrolysis by using cellulase. The recombinant CgAA9 (0.9 mg/g cellulose) exhibited 1.7-fold synergism in the hydrolysis of Avicel when incubated with 0.9 filter paper units of Celluclast 1.5 L/g cellulose. The first study of the active expression of AA9 using a bacterial host and its synergistic optimization could be useful for the industrial application of AA9 for the saccharification of lignocellulose.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-015-6592-3) contains supplementary material, which is available to authorized users.
Highlights
Lignocellulose is a promising feedstock for the production of biofuels or biochemicals
Induction of the expression of CHGG_09805, a candidate gene for auxiliary activity 9 (AA9), by cellulosic substrates was examined by reverse transcription-polymerase chain reaction (RT-PCR)
The band intensities for the amplified complementary DNA (cDNA) genes of CHGG_09805 from C. globosum grown on cellulose were higher than that for C. globosum grown on glucose when qualitatively visualized (Fig. 1)
Summary
Lignocellulose is a promising feedstock for the production of biofuels or biochemicals. The role of nonhydrolytic proteins in cellulose hydrolysis was proposed in the C1–Cx model several decades ago, in which the C1 factor (non-hydrolytic protein) acts as an enhancing protein for the Cx factor (hydrolytic enzyme) (Din et al 1994; Gilligan and Reese 1954; Reese et al 1950). Synergism between nonhydrolytic proteins and hydrolytic enzymes has been observed with carbohydrate-binding modules (CBMs), bacterial expansin, swollenin, and auxiliary activity 9 (AA9) (Dimarogona et al 2012; Din et al 1991; Harris et al 2010; Kim et al 2009; Lin et al 2013; Suwannarangsee et al 2012; Zhou et al 2011). It has been found that fungal AA9 and AA10 (CBM33) possess synergistic activity with cellulase and act by chemically modifying cellulose (Forsberg et al 2011; Langston et al 2011; Phillips et al 2011a; Quinlan et al 2011; Vaaje-Kolstad et al 2010)
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