Exploration of fragment-derived modulators of glycoside hydrolases

Previous work at York demonstrated that fragment molecules can increase the activity of the glycoside hydrolase, BtGH84. The initial aim of this project was to use fragment-based discovery methods to identify activators of several enzymes used in cellulose degradation where low activity is one of the limiting steps in the industrial process. This was successful for one enzyme, the fungal glycoside hydrolase, TrBgl2. The characterisation of the mechanism of activation for this enzyme is the main focus of this thesis. A fragment screen of a library of 560 commercially available fragments using a kinetic assay identified a small molecule activator of TrBgl2. An analogue by catalogue approach and detailed kinetic analysis identified compounds that behaved as nonessential activators with up to a 2-fold increase in maximum activation. The compounds did not activate the related bacterial glycoside hydrolase CcBglA demonstrating specificity. Interestingly, an analogue of the initial fragment inhibits both TrBgl2 and CcBglA, apparently through a mixed-model mechanism. Although it was not possible to determine crystal structures of activator binding to 55 kDa TrBgl2, solution NMR experiments demonstrated a specific binding site for the activator. A partial assignment of the NMR spectrum gave the identity of the amino acids at this site, allowing a model for TrBgl2 activation to be built. The activator binds at the entrance of the substrate binding site, stabilizing the enzyme-substrate complex.