Functional characterization of a bacterial expansin from Bacillus subtilis for enhanced enzymatic hydrolysis of cellulose.
Expansin is a plant protein family that induces plant cell wall-loosening and cellulose disruption without exerting cellulose-hydrolytic activity. Expansin-like proteins have also been found in other eukaryotes such as nematodes and fungi. While searching for an expansin produced by bacteria, we found that the BsEXLX1 protein from Bacillus subtilis had a structure that was similar to that of a beta-expansin produced by maize. Therefore, we cloned the BsEXLX1 gene and expressed it in Escherichia coli to evaluate its function. When incubated with filter paper as a cellulose substrate, the recombinant protein exhibited both cellulose-binding and cellulose-weakening activities, which are known functions of plant expansins. In addition, evaluation of the enzymatic hydrolysis of filter paper revealed that the recombinant protein also displayed a significant synergism when mixed with cellulase. By comparing the activity of a mixture of cellulase and the bacterial expansin to the additive activity of the individual proteins, the synergistic activity was found to be as high as 240% when filter paper was incubated with cellulase and BsEXLX1, which was 5.7-fold greater than the activity of cellulase alone. However, this synergistic effect was observed when only a low dosage of cellulase was used. This is the first study to characterize the function of an expansin produced by a non-eukaryotic source.
Kim
Eun Sil
ES
School of Life Sciences & Biotechnology, Korea University, Seoul 136-713, Republic of Korea.
Lee
Hee Jin
HJ
Bang
Won-Gi
WG
Choi
In-Geol
IG
Kim
Kyoung Heon
KH
D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002480:Cellulase / Q000378:metabolism; D002482:Cellulose / Q000378:metabolism*; D003001:Cloning, Molecular; D004798:Enzymes / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D006868:Hydrolysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010209:Paper; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D004798:Enzymes; D011994:Recombinant Proteins; D002482:Cellulose; D002480:Cellulase