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Title page for ETD etd-07082012-104208


Type of Document Dissertation
Author Taylor, Courtney Barnett
URN etd-07082012-104208
Title Investigating structure-function relationships in family 7 cellulases by molecular simulation
Degree PhD
Department Chemical Engineering
Advisory Committee
Advisor Name Title
Dr. Clare McCabe Committee Chair
Dr. Eugene LeBoeuf Committee Member
Dr. Kenneth Debelak Committee Member
Dr. Peter T. Cummings Committee Member
Keywords
  • celluases
  • molecular simulation
  • biofuels
  • thermodynamic integration
Date of Defense 2012-06-18
Availability unrestricted
Abstract
The conversion of plant biomass to fermentable sugars is a primary option for the production of biofuels. Cellulases, the enzymes that break down recalcitrant plant cellulose materials into fermentable sugars, can be utilized in the commercial production of biofuels if throughput can be increased and costs reduced. Understanding the molecular-level actions of cellulases is a significant challenge that must be overcome to improve cellulase productivity and efficiency in biofuel production. Here we use molecular simulation to probe how cellulases identify and bind to crystalline cellulose and how this may be improved. The systems studied are synergistic, highly active, and well-characterized enzymes Cellobiohydrolase I (Cel7A) and Endoglucanase-I (EG1 or Cel7B) produced by the filamentous fungi Trichoderma reesei. Both of these enzymes are multi-domain, consisting of a carbohydrate binding domain (CBM), a large catalytic domain, and a connective linker peptide. In particular, we study the addition of glycans, or sugars, to the Cel7A CBM and our results suggest that changing the sugar patterns (known as glycosylation) positively impacts binding affinity by 500-fold (up to 3.8 kcal/mol). This is potentially a new direction in protein engineering in that modifying glycosylation patterns via genetic and chemical synthesis or culture manipulation can alter CBM binding affinity to carbohydrates and may thus be a general strategy to enhance cellulase performance. We also utilize molecular simulation to highlight the functional differences in the catalytic domains of Cel7A, which breaks down cellulose chains processively, and Cel7B, which randomly cleaves glycosidic bonds on the cellulose surface. By investigating the impact of protein conformational changes and aromatic mutations in the active sites of these enzymes, we offer insights into the energetics and structure-function relationships necessary for binding. In general the results of the simulations performed provide insights that could aid in the efforts to rationally engineer cellulase enzymes with improved performance in biofuel production.
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