Binding characteristics of a bacterial expansin ( Bs EXLX1) for various types of pretreated lignocellulose
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BIOTECHNOLOGICALLY RELEVANT ENZYMES AND PROTEINS
Binding characteristics of a bacterial expansin (BsEXLX1) for various types of pretreated lignocellulose In Jung Kim & Hyeok-Jin Ko & Tae-Wan Kim & Ki Hyun Nam & In-Geol Choi & Kyoung Heon Kim
Received: 23 July 2012 / Revised: 16 August 2012 / Accepted: 22 August 2012 / Published online: 29 September 2012 # Springer-Verlag Berlin Heidelberg 2012
Abstract BsEXLX1 from Bacillus subtilis is the first discovered bacterial expansin as a structural homolog of a plant expansin, and it exhibited synergism with cellulase on the cellulose hydrolysis in a previous study. In this study, binding characteristics of BsEXLX1 were investigated using pretreated and untreated Miscanthus x giganteus in comparison with those of CtCBD3, a cellulose-binding domain from Clostridium thermocellum. The amounts of BsEXLX1 bound to cellulose-rich substrates were significantly lower than those of CtCBD3. However, the amounts of BsEXLX1 bound to lignin-rich substrates were much higher than those of CtCBD3. A binding competition assay between BsEXLX1 and CtCBD3 revealed that binding of BsEXLX1 to alkali lignin was not affected by the presence of CtCBD3. This preferential binding of BsEXLX1 to lignin could be related to root colonization in plants by bacteria, and the bacterial expansin could be used as a lignin blocker in the enzymatic hydrolysis of lignocellulose. Electronic supplementary material The online version of this article (doi:10.1007/s00253-012-4412-6) contains supplementary material, which is available to authorized users. I. J. Kim : H.-J. Ko : I.-G. Choi : K. H. Kim (*) School of Life Sciences and Biotechnology, Korea University, Seoul 136-713, South Korea e-mail: [email protected] T.-W. Kim Energy Biosciences Institute, Berkeley, CA 94720, USA K. H. Nam Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14850, USA
Keywords Bacterial expansin . BsEXLX1 . Binding . Cellulose . Lignin . Lignocellulose . Miscanthus x giganteus
Introduction The enzymatic hydrolysis of cellulose into glucose is a key step in utilizing lignocellulose for biofuel production since obtaining fermentable sugar at low cost is critical for the commercial success of biofuels (Lynd et al. 2008; Bak et al. 2009). The enzymatic conversion of lignocellulose into sugars is inherently difficult; accordingly, many approaches have been taken to facilitate this process. These include efforts to develop and employ highly active cellulases (Graham et al. 2011; Kim et al. 2011; Merino and Cherry 2007), accessory proteins that have nonhydrolytic activity during the hydrolysis of cellulose (Kim et al. 2009; Suwannarangsee et al. 2012), and enzymes that bind weakly to lignin (Berlin et al. 2005). The search for synergistic accessory proteins in particular has recently attracted a great deal of attention. Indeed, several studies have investigated the synergism of cellulase with nonhydrolytic proteins such as plant expansins (Cosgrove 2001), nonplant expansin-like proteins including BsEXLX1 from Baci
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