Monday, May 4, 2009
12-27
Synergism of a bacterial expansin, BsEXLX1 with the catalytic doamin endo-β-1,4-glucanase in cellulose hydrolysis
The expansin is the plant cell wall protein which is known to induce the extension of plant cell wall polysaccharides in plant growth. Expansins are receiving much attention due to their application potential since they are also found to have a synergistic effect on enzymatic hydrolysis of cellulose when used in combination with cellulase. However, the expression of plant expansins in organisms other than plants has not been reported yet. Recently, we characterized the structural expansin homologs from bacteria and found that they had synergistic activity for cellulose hydrolysis by cellulase in addition to binding and weakening activities for cellulose (Kim, E. S. et al., J. Biotechnol. 136S: S426, 2008; H. J. Lee et al., J. Biotechnol. 136S: S343, 2008; Kim, E. S. et al., Biotechnol. Bioeng., in press). In this study, important characteristics of BsEXLX1, which was cloned from Bacillus subtilis and overexpressed in E. coli, were investigated. In the adsorption isotherm study of BsEXLX1 using Avicel, the binding activity was dependent on both pH and temperature, and it also showed binding activity to other polysacchartides such as agarose, starch, and xylan. When a catalytic domain of endo-1,4-β-glucanase was used with BsEXLX1 for cellulose hydrolysis, the hydrolysis by endo-1,4-β-glucanase was promoted by BsEXLX1. This is the first to study of the bacterial expansin for its adsorption isotherm and synergism with cellulase containing a catalytic domain only.
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