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Computational Thermostable Cellulase Engineering for Enhanced Biofuel Production

By Toni Lee, Mary Farrow, Frances Arnold and Stephen Mayo

Abstract

Generating biofuels from cellulosic material may\ud mitigate the detrimental environmental effects of\ud current production schemes. Common agricultural\ud byproducts and algal feedstocks are cellulosic in nature,\ud providing more biomass than grain sources while\ud minimizing agricultural intensification. Employing\ud cellulosic feedstocks, however, requires the use of\ud relatively expensive cellulases, enzymes capable\ud of cleaving cellulose into fermentable sugars. One\ud method of reducing cellulase cost relies on an idea\ud encapsulated in the Arrhenius equation, that reaction\ud rates increase as temperature increases. Employing\ud thermostable cellulases would not only minimize\ud process time, but would also reduce the amount of\ud enzyme necessary per gallon of synthesized fuel.\ud We are currently computationally engineering\ud hyperthermostable variants of Cel5A from the fungus\ud Hypocrea jecorina (Hj_ Cel5A), one of the most heavily\ud employed cellulases in the biofuels industry. To obtain a\ud starting scaffold for design purposes, we have recently\ud solved the structure of this enzyme. When compared\ud to a thermostable homolog, the Hj_Cel5A structure\ud demonstrates long, solvent-exposed loops. As such, we\ud are combining traditional core-repacking algorithms\ud with loop truncation software to generate thermostable\ud variants. To ensure loop truncation does not disrupt\ud protein stability, we utilize an algorithm to predict\ud loop trajectories around the mutated sites, and then\ud perform sequence optimization on the new structure.\ud Here we present the crystal structure of H. jecorina\ud Cel5A to 2.1 Å, data demonstrating the robustness of\ud our design methodology, and preliminary designs that\ud await biochemical testing

Publisher: Wiley
Year: 2012
OAI identifier: oai:authors.library.caltech.edu:33535
Provided by: Caltech Authors
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