Glycosidase inhibitors as conformational transition state analogues

Catalytic mechanism of cellulose degradation by a cellobiohydrolase, CelS

The hydrolysis of cellulose is the bottleneck in cellulosic ethanol production. The cellobiohydrolase CelS from Clostridium thermocellum catalyzes the hydrolysis of cello-oligosaccharides via inversion of the anomeric carbon. Here, to examine key features of the CelS-catalyzed reaction, QM/MM (SCCDFTB/MM) simulations are performed. The calculated free energy profile for the reaction possesses a 19 kcal/mol barrier. The results confirm the role of active site residue Glu87 as the general acid catalyst in the cleavage reaction and show that Asp255 may act as the general base. A feasible position in the reactant state of the water molecule responsible for nucleophilic attack is identified. Sugar ring distortion as the reaction progresses is quantified. The results provide a computational approach that may complement the experimental design of more efficient enzymes for biofuel production.

Mechanistic insights into glycosidase chemistry

The enzymatic hydrolysis of the glycosidic bond continues to gain importance, reflecting the critically important roles complex glycans play in health and disease as well as the rekindled interest in enzymatic biomass conversion. Recent advances include the broadening of our understanding of enzyme reaction coordinates, through both computational and structural studies, improved understanding of enzyme inhibition through transition state mimicry and fascinating insights into mechanism yielded by physical organic chemistry approaches.