Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
The binding affinity of carbohydrate-binding modules (CBMs) to cellulose in cellulases is known to be proportional to enzyme activity, making binding affinity an important parameter in improving performance. We use molecular simulation to quantify cellulose binding of a natively-glycosylated Family 1 CBM and demonstrate that enhanced binding of 3-fold over a non-glycosylated CBM is achieved by the addition of a single, native mannose. Such modifications to the CBM have not been considered previously experimentally or computationally. Furthermore, we extend the study to investigate the impact of common O-glycosylation patterns found in other fungi by studying mannose dimers, trimers, and branched structures, as well as glucose-based glycans. We predict increases in relative binding affinity of 6- to over 200-fold for these simple O-glycans over the non-glycosylated CBM, suggesting that both the glycan linkage patterns and glycan chemistry affect the interaction with cellulose. Generally, our results suggest that CBM binding studies should consider the effects of glycosylation on binding and function, but these results also indicate potential new directions in protein engineering, in that modifying glycosylation patterns via heterologous expression, manipulation of culture conditions, or introduction of artificial glycosylation sites, can alter CBM binding affinity to carbohydrates and may thus be a general strategy to enhance cellulase performance.