P6: Study on Synergism between Cucumber α-Expansin and Fungal Endoglucanase and Pectin Lyase

Several recombinant fungal enzymes (endoglucanase and pectinase) were studied for their interactions with α-expansin in cell wall extension and polysaccharide degradation. Both Cel12A and Cel5A were able to hydrolyze cellulose CMC-Na and mixed-linkage β-glucan. Different from Cel5A, Cel12A could also hydrolyze xyloglucan and induce wall extension of cucumber hypocotyls in an in vitro assay. Combining α-expansin, even at high concentrations, with Cel12A did not enhance the maximum/final wall extension rate induced by Cel12A alone. These results strongly suggest that modification/degradation of xyloglucan molecule/network is the key for cell wall extension, and α-expansin and Cel12A may share the same acting site in the substrate. Pectinase (Pel1, a pectin lyase) could enhance α-expansin-induced wall extension in a concentration-dependent manner, suggesting that the pectin network may normally regulate accessibility of expansin to xyloglucan-cellulose complex. α-Expansin enhanced Cel12A’s hydrolytic activity on cellulose CMC-Na but not on xyloglucan and β-glucan. Expansin did not affect Cel5A’s hydrolytic activity. Interestingly, expansin could also enhance Pel1’s activity on degrading high esterified pectin. The potential explanation for why expansin could synergistically interact with only certain enzymes on specific polysaccharides was discussed. Additional results also suggested that cell wall swelling may not be a significant event during the action of expansin and hydrolases.
Keywords: cell wall, endoglucanase, Expansin, pectin lyase, xyloglucan
Acknowledgements: this work was supported by the National Natural Science Foundation of China (30770032) to Sheng Yuan and by the South Dakota Agricultural Experiment Station at South Dakota State University to Yajun Wu.