Centre de Biotechnologie de Sfax, University of Sfax, Sfax, Tunisia.
Carbohydr Res. 2011 Sep 27;346(13):1848-54. doi: 10.1016/j.carres.2011.06.016. Epub 2011 Jul 19.
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.
串珠镰刀菌是一种丝状真菌，可产生各种β-葡萄糖苷酶，其中两种已被鉴定。本研究报告了在仅以 d-葡萄糖作为碳源的情况下，产生第三种β-葡萄糖苷酶（命名为 bglG）的情况，以及随后的纯化和表征。尽管在 d-葡萄糖存在下可以有效地产生 bglG，但该酶仍受到该糖的高度抑制。事实上，添加 d-葡萄糖会显著降低 pNPG 水解过程中的葡萄糖生成速率。这项工作报告了各种碳水化合物对 bglG 活性的影响，以了解 d-葡萄糖抑制该酶的机制。研究结果表明，bglG 受到 d-葡萄糖（相对活性的 44%，在 5mM 时）、d-山梨醇（相对活性的 96%）、d-甘露糖（相对活性的 56%）、纤维二糖和麦芽糖（相对活性的 72%和 71%）的强烈抑制。另一方面，d-半乳糖、d-果糖、乳糖和蔗糖对 bglG 活性没有影响。同样，一些异构体，如 2-乙酰氨基-2-脱氧-d-葡萄糖和 2-脱氧-d-阿拉伯己糖（2-脱氧-d-葡萄糖），对 bglG 的相对活性没有任何影响。另一方面，d-木糖和木糖醇分别将 bglG 活性提高至相对活性的 123%和 120%。因此，构型、差向异构化、异构化和取代在 bglG 抑制中起关键作用。还研究了铁（bglG 的最佳激活剂，161%）与其中一些添加剂组合的效果。研究结果表明，虽然铁在 10mM 浓度下与 d-葡萄糖结合使用会导致 bglG 抑制作用降低两倍（在 5mM 时为 84%），但铁对其余测试添加剂仍保持相同的作用。
