Hydroxyl distribution in sugar structure and its contributory role in the inhibition of Stachybotrys microspora β-glucosidase (bglG).

Stachybotrys microspora is a filamentous fungus that produces various β-glucosidases, of which two have already been characterized. The present study reports on the production of a third one, named bglG, in the presence of d-glucose used as a sole carbon source, and on its subsequent purification and characterization. Although efficiently produced in the presence of d-glucose, bglG continues to be highly inhibited by this sugar. In fact, the addition of d-glucose significantly decreases the glucose formation rates during the hydrolysis of pNPG. This work reports on the effect of various carbohydrates on bglG activity in order to understand the mechanisms adopted by d-glucose to inhibit this enzyme. The findings indicate that bglG is strongly inhibited by d-glucose (44% of the relative activity at 5mM), d-glucitol (96% of the relative activity), d-mannose (56% of the relative activity), cellobiose and maltose (72% and 71% of the relative activity, respectively). On the other hand, d-galactose, d-fructose, lactose, and sucrose have no effect on bglG activity. Similarly, several isomers, such as 2-acetamido-2-deoxy-d-glucose and 2-deoxy-d-arabino-hexose (2-deoxy-d-glucose) were noted to bring no change on the relative activity of bglG. d-xylose and xylitol, on the other hand, enhanced bglG activity up to 123% and 120% of relative activity, respectively. Accordingly, the configuration, epimerisation, isomerisation, and substitutions played key roles in bglG inhibition. The effect of the combination of iron (the best activator of bglG, 161%) with some of those additives was also investigated. The findings revealed that, while a combination of iron at a concentration of 10mM with d-glucose resulted in a two-fold decrease in bglG inhibition (84% at 5mM), iron maintained the same effect with the remainder of the additives being tested.