Natural and designed enzymes for cellulose degradation

Abstract

Biofuels hold significant promise as an environmentally friendly means to displace a significant amount of fossil fuel from the global liquid transportation fuel mix. Compared with current corn and sugarcane-based feedstocks, which are agriculturally intensive, lignocellulosic feedstocks are abundant, can be produced cheaply, and have a much smaller carbon footprint per unit energy output. However, conversion of cellulosic materials into simple sugars (an intermediate step in biofuel production) is a significant challenge, owing to the rigidity and high resistance of cellulose to degradation. Recent efforts to improve enzymatic breakdown of cellulose have taken advantage of expanding genome sequence databases, advances in structural biology of cellulose degradation enzymes (cellulases), biochemical studies of enzymatic breakdown of cellulose, and protein engineering studies. In this chapter, the structural features of cellulose and cellulose-degrading enzymes will be reviewed, along with methods used to determine cellulase activity. We will focus on models for synergistic effects among enzymes, strategies used by bacteria and fungi to increase reactivity through synergistic enhancement, and approaches by which synergistic enhancement can be engineered into artificial enzymes to be used for large-scale cellulose-based biofuels production.