5-04: Characterization of novel bacterial expansins that promote enzymatic hydrolysis of plant cell wall polymers

Plan cell wall polymers, which are considered to be the most abundant renewable resource on earth, are mainly composed of cellulose, hemicellulose and lignin. Due to the recalcitrance of cellulose itself and the protective barriers of lignin, the enzymatic hydrolysis of cellulose and hemicellulose to obtain sugars has long been a challenge.  In the process of cell growth, a plant cell wall protein, expansin, is found to be involved in inducing extension of cell wall without hydrolysis.  In our study, the functions of novel expansins from bacterial sources, which are the structural homologs of maize expansin, EXPB1, were targeted and elucidated for the first time in this area (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) since expansins only from eukaryotic sources such as plants, animals or fungi were so far functionally characterized.  Many eucarytic expansins were found, but none of their overexpression in microorganisms has been successful yet.  The bacterial expansins expressed in a soluble form in the present work showed binding and weakening activities towards cellulose or xylan and also exhibited significant synergistic activity with enzymes in the hydrolysis of cellulose or xylan.  These findings might have opened a door to the possible applications of bacterial expansins in effective enzymatic conversion of lignocellulosic biomass into sugars.