Monday, May 4, 2009
12-28
Functional analysis of a bacterial expansin from Hahella chejunsis for promoting hydrolysis of xylan
Expansins are plant cell wall proteins that are known to involve in extension of cell wall during plant growth, and it is presumably considered to be induced by disrupting hydrogen bonds within the cell wall polymer matrix. The cell wall-loosening activity gives high potential for effective deconstruction of lignocellulose that is the main component of plant cell wall. Due to the difficulty of expression of plant expansin in hosts other than plant, bacterial expansins are receiving increasing attention (H. J. Lee et al., J. Biotechnol. 136S: S343, 2008; Kim, E. S. et al., Biotechnol. Bioeng., in press). Previously, we identified a bacterial expansin in Hahella chejunsis (HcEXLX) based on its amino acid sequence homology with BsEXLX1, a bacterial expansin from Bacillus subtilis, where the molecular function of HcEXLX was initially unknown and annotated as a hypothetical protein (H. J. Lee et al., J. Biotechnol. 136S: S343, 2008). HcEXLX was overexpressed in E. coli in a soluble form at 30 mg/L, and the bacterial expansin was found to bind various polysaccharides such as Avicel, BMCC, xylan from oats spelt slightly (12%). In addition to the synergistic activity toward cellose hydrolysis with cellulase, HcEXLX showed a synergistic effect (~ 300% compared with the control without HcEXLX) in the hydrolysis of xylan (from oat spelt) by xylanase. This is the first report showing the synergistic effect of a bacterial expansin on hydrolysis of xylan.
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