The recalcitrance of cellulose, coupled with non-productive binding of cellulases, is considered to be a major bottleneck in the deconstruction of biomass into biofuels (Jeoh, T., Cardona, M. J., Karuna, N., Mudinoor, A. R. & Nill, J. Mechanistic kinetic models of enzymatic cellulose hydrolysis—A review. Biotechnol. Bioeng. 114, 1369–1385 (2017). doi:10.1002/bit.26277). Past research to address the recalcitrance of cellulose, has led the development of pre-treatment technologies like the Extractive Ammonia process (Sousa, L. et al. Next-generation ammonia pretreatment enhances cellulosic biofuel production. Energy Environ. Sci. 9, 1215–1223 (2016). doi:10.1039/c5ee03051j), which can modify the ultrastructure of native crystalline cellulose-I to cellulose-III allomorph (Chundawat, S. P. S. et al. Restructuring the crystalline cellulose hydrogen bond network enhances its depolymerization rate. J. Am. Chem. Soc. 133, 11163–11174 (2011). doi:10.1021/ja2011115). Surprisingly, it was found previsouly that some full-length cellulases bind with lower apparent affinity to crystalline cellulose-III, while the enzymatic hydrolysis rate for this modified cellulose-III allomorph was between two to five-folds higher by fungal cellulase enzyme cocktails (Gao, D. et al. Increased enzyme binding to substrate is not necessary for more efficient cellulose hydrolysis. Proc. Natl. Acad. Sci. 110, 10922–10927 (2013). doi:10.1073/pnas.1213426110). Our results attest to better understanding the role of carbohydrate-binding modules (CBMs) on the reduced binding affinity of full-length fungal cellulases seen towards cellulose-III. Here, we closely explore the role of key amino acid residues of a Family 1 CBM that are likely to impact protein binding interactions with the surface of cellulose-III. Single-site saturation mutagenesis libraries were generated at such key positions to better understand impact on CBM-1 adsorption to both cellulose allomorphs. We report results here relating to the: (i) Expression and purification of green fluorescent protein (GFP) tagged wild-type CBM-1 protein construct and its single-site saturation mutagenesis protein library for subsequent binding/structural characterization, (ii) Effect of pH and salt concentration on the apparent binding affinity or partition coefficient of wild-type CBM-1 protein and its saturation mutagenesis mutants library towards cellulose allomorphs. We also report regression correlations between the experimentally measured binding parameters and various in silico sequence/structural modeling derived Rosetta software estimated parameters that are indicative of protein function. We also discuss a roadmap for future studies that include analysis of full scale binding isotherm of wild type and some of the key mutants to native and pre-treated cellulose, cloning and testing of overall cellulase activity with mutant CBM1-cellulases to understand the correlation between CBM-mediated overall binding affinity and cellulolytic activity on different cellulose allomorphs. This work has important implications for creation of more efficient cellulase enzymes, which can pave the way towards sustainable production of biofuels from ammonia-pretreated lignocellulosic biomass.
Subject (authority = RUETD)
Topic
Chemical and Biochemical Engineering
Subject (authority = LCSH)
Topic
Carbohydrates—Biodegradation
Subject (authority = LCSH)
Topic
Biomass energy
RelatedItem (type = host)
TitleInfo
Title
Rutgers University Electronic Theses and Dissertations
Identifier (type = RULIB)
ETD
RelatedItem (type = host)
TitleInfo
Title
School of Graduate Studies Electronic Theses and Dissertations
Identifier (type = local)
rucore10001600001
Identifier
ETD_9323
Identifier (type = doi)
doi:10.7282/T3MG7T4W
PhysicalDescription
Form (authority = gmd)
electronic resource
InternetMediaType
application/pdf
InternetMediaType
text/xml
Extent
1 online resource (xi, 79 pages : illustrations)
Note (type = degree)
M.S.
Note (type = bibliography)
Includes bibliographical references
Note (type = statement of responsibility)
by Akash Dagia
Location
PhysicalLocation (authority = marcorg); (displayLabel = Rutgers, The State University of New Jersey)
I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.