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Cloning, Expression and Characterization of New Bacterial Endoglucanases with High Thermostability

Author: QiuLiHuan
Tutor: XuJianHe
School: East China University of Science and Technology
Course: Microbiology
Keywords: endoglucanase (EG) cloning and expression Escherichia coli thermostability characterization
CLC: Q78
Type: Master's thesis
Year: 2011
Downloads: 22
Quote: 0
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Abstract


Cellulose is one of the most abundant renewable bioresources. It is the primary and main constituent of plants with an annual production estimated at 100 billion dry tons. Cellulases can convert cellulose to glucose efficiently under mild conditions, but currently the enzymatic hydrolysis of cellulose is still suffering from several severe disadvantages such as slow rate and low efficiency. The search for celluases with high activity and/or high thermostability is an important way to address these issues. It is well known that the synergisitic interactions among three main cellulases, i.e., endoglucanase, exoglucanase andβ-glucosidase, could convert cellulose into glucose, an easily fermentable sugar. Endoglucanase (EG) is believed to play an important role in such a process.EGs are widely distributed among bacteria, fungi, and plants. As many as 43 genes encoding putative endoglucanases were chosen from the database of Swiss-prot. All these genes come from various bacteria,22 of which were then successfully expressed in E. coli BL21/pET-43.1a. Among them,15 enzymes showed significant activity towards carboxymethyl cellulose (CMC) as a standard substrate. Three enzymes with higher activity, EGtfl (Q08166), EGtf2 (Q7X2N2) and EGbs (B6DVJ2), have been purified to homogeneity and characterized of biocatalytic properties. The purified enzymes exhibited the highest activity around 55℃and pH 5.0. With high thermal stability, enzymes EGtfl and EGtf2 kept active after being incubated at 50℃for more than 1000 h, almost 100-fold higher than the other reviewed EGs. Furthermore, the presence of various metal ions or organic solvents did not cause significant effect on the activities of EGtfl and EGtf2, and these two enzymes even showed 2.1-and 2.7-fold enhancement in the presence of dodecanol. All these features, especially the outstanding thermostability, enable the bacterial enzymes EGtfl and EGtf2 as a platform for further protein engineering to realize ultimate practical application.

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