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The Zhang Lab |
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Driving Tomorrow by Biomass Sugarsthrough Imagination, Invention and Innovation
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Research Interests
Courses Taught BSE 5984 Enzyme Engineering (fall 2008, 2010) Research Statement
1. Cellulose solvent- and organic solvent-based lignocellulose fractionation (COSLIF) Technology
In addition, we have developed Version 2 and 3 lignocellulose fractionation, which have solved two main shortcomings of Version 1 -- reducing solvent use volume by several fold and avoiding dilute sugar reconcentration. This technology has been successfully applied to numerous feedstocks, such as corn stover, switchgrass, poplar, industrial hemp hurds, bamboo, common reed, etc. Furthermore, this technology can drastically decrease costly cellulase use for efficient glucan hydrolysis [2-4].
2. Cellulase Engineering via Biomolecular Engineering The improvement of specific cellulase activities can be implemented through cellulase engineering -- rational design and directed evolution for each cellulase component as well as the reconstitution of cellulase components [5]. We are applying the combinatorial technologies involving DNA mutagenesis techniques, enzyme cell surface display techniques, and evolutionary engineering for improving cellulase activity on insoluble substrate cellulose. Recently, we have improved beta-glucosidase thermostability and catalytic efficiency by directed evolution [6]. 3. Cellulose hydrolysis mechanisms mediated by cellulase, cellulosome, and cellulolytic microbes Cellulose biodegradation requires three types of cellulases (endoglucanase, exoglucanases, and beta-glucosidase) to work together [7]. The unidentified characteristics of heterogeneous cellulose, the complicated interaction between solid cellulose and cellulase components, and the synergic/competitive relationship among various cellulase components limit our understanding of this de-polymerization process and also lags behind the developments in lignocellulose pretreatment and cellulase improvement. We have developed a generic functionally based mathematical model to simulate this complicated process [8]. A new rapid method has been developed to determine the degree of polymerization of cellulose [9]; a new kind of non-substitution, high reactivity, homogeneous, regenerated amorphous cellulose (RAC) has been prepared for studying cellulose hydrolysis [10]. Now we are developing several new technologies which will help us to characterize key substrate characteristics, and elucidate in-depth mechanisms that will provide new insights into lignocellulose pretreatment and cellulase improvement. In addition, we have discovered a new cellulose hydrolysis mechanism for microbial cellulose hydrolysis mediated by a complexed cellulase system -- the Clostridium thermocellum cellulosome [11,12]. 4. Enzymatic hydrogen production by cell-free synthetic enzymatic
biotransformation[13,14]
What is more important, the integration of this technology with PEM fuel cell would achieve the highest energy efficiency from chemical energy to mechanical energy. The details of life cycle analysis pertaining to the carbohydrate hydrogen economy vs other hypocretical future economies, such as methanol economy, electron economy, are being conducted.
See Our Vision about the Future Transportation and Energy Storage .
References [1] Zhang Y.-H.P., Ding S.-Y., Mielenz J.R., Cui J.-.B., Elander R.T., Laser M, Himmel M.E., McMillan, J.D., Lynd, L.R. 2007. Fractionating recalcitrant lignocellulose at modest reaction conditions. Biotechnology and Bioengineering 97(2): 214-223. [2] Moxley G, Zhu Z, Zhang Y-HP*. 2008. Efficient sugar release by the cellulose solvent-based lignocellulose fractionation technology and enzymatic cellulose hydrolysis. Journal of Agriculture and Food Chemistry 56: 7885–7890 (PDF) [3] Zhu Z, Sathitsuksanoh N, Vinzant T, Schell DJ, McMillan JD, Zhang Y-HP*. 2009. Comparative study of corn stover pretreated by dilute acid and cellulose solvent-based lignocellulose fractionation: Enzymatic hydrolysis, supramolecular structure, and substrate accessibility. Biotechnology and Bioengineering (Epub, PDF). [4] Sathitsuksanoh N, Zhu Z, Templeton N, Rollin J, Harvey S, Zhang Y-HP*. 2009. Saccharification of a potential bioenergy crop, Phragmites australis (common reed), by lignocellulose fractionation followed by enzymatic hydrolysis at decreased cellulase loadings. Industrial & Engineering Chemistry Research (accepted). [5] Zhang Y.-H.P., Himmel E. M., Mielenz J.R. 2006. Outlook for cellulase improvement: Screening and selection strategies. Biotechnology Advances, 22(5): 452-481. [6] Liu W, Hong J, Bevan DR, Zhang Y-HP*. 2009. Fast identification of thermostable beta-glucosidase mutants on cellobiose by a novel combinatorial selection/screening approach. Biotechnology and Bioengineering (Epub, PDF). [7] Zhang Y.-H.P., and Lynd L.R. 2004. Toward an aggregated understanding of enzymatic hydrolysis of cellulose: non-complexed cellulase systems. Biotechnology and Bioengineering 88:797-824. [8] Zhang Y.-H.P., Lynd L.R. 2006. A functionally-based model for hydrolysis of solid cellulose by fungal cellulase. Biotechnology and Bioengineering, 94(5): 888-898. [9] Zhang Y.-H.P., and Lynd L.R. 2005. Determination of the number average degree of polymerization of cellodextrins and cellulose with application to enzymatic cellulose hydrolysis Biomacromolecules 6: 1510-1515. [10] Zhang Y.-H.P., Cui X.B., Lynd L.R., and Huang L. 2006. A transition from cellulose swelling to cellulose dissolution by o-phosphoric acid: Evidences from supramolecular structures and enzymatic hydrolysis. Biomacromolecules 7(2): 644-648. [11] Zhang Y.-H.P., and Lynd L.R. 2005. Cellulose utilization by Clostridium thermocellum: bioenergetics and hydrolysis product assimilation. Proceedings of the National Academy of Sciences of USA 102:7321-7325. [12] Lu Y.P., Zhang Y.-H.P., Lynd L.R. 2006. Evidence for enzyme-microbe synergy in cellulose utilization by Clostridium thermocellum. Proceedings of the National Academy of Sciences of USA 103(44): 16165-16169. [13] Zhang Y.-H.P., Mielenz J.R., Evans B.R., Hopkins R.C., Adams M.W.W. 2007. High-yield hydrogen production from starch and water by synthetic enzymatic pathway. PLOS ONE 2(5): e456. [14] Ye X, Wang Y, Hopkins RC, Adams MWW, Evans BR, Mielenz JR, Zhang Y-HP*. 2009. Spontaneous high-yield hydrogen generation from cellulosic materials catalyzed by enzyme cocktails. ChemSusChem 2:149-152. (PDF). [15] Zhang Y-HP*. 2009. A sweet out-of-the-box solution for the hydrogen economy: Is sugar-powered car science fiction? Energy Environmental Science 2: 272-282 (PDF). Research Support
If you are interested in our technology transfer (lignocellulose fractionation and enzymatic hydrogen production), please feel free to contact me or VTIP. Imagination, Innovation, Implementation (3I Biofuels Lab) |
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