Novel β-Glucosidase Mibgl3 from Microbacterium sp. XT11 with Oligoxanthan-Hydrolyzing Activity

The enzymatic pathway of xanthan depolymerization has been predicted previously; however, the beta-glucosidase and unsaturated glucuronyl hydrolase in this system have not been cloned and characterized. This lack of knowledge hinders rational modification of xanthan and exploration of new applications. In this work, we report on the properties of Mibgl3, a xanthan-degrading enzyme isolated from Microbacterium sp. XT11. Mibgl3 exhibits typical structural features of the GH3 family but shares low sequence identity with reported GH3 enzymes. The activity of Mibgl3 can be inhibited by Cu2+, Fe2+, Zn2+, and glucose. Unlike most beta-glucosidases, Mibgl3 can tolerate a wide pH range and is activated by high concentrations of NaCI. This improves the commercial value of Mibgl3. In particular, Mibgl3 exhibits higher substrate specificity toward oligoxanthan than other beta-glucosidases. Ion chromatography, ultrahigh-performance liquid chromatography-mass spectrometry (UPLC-MS), and GC-MS results showed that Mibgl3 could effectively hydrolyze oligoxanthan to release glucose and glucuronate. Therefore, Mibgl3 might play an important role in xanthan depolymerization by functioning as hydrolase of both the xanthan backbone and sidechains. This knowledge of the enzymatic properties and hydrolysis mechanism of a beta-glucosidase will be beneficial for future applications.

Automated summary

This study reports the properties of a xanthan-degrading enzyme called Mibgl3, isolated from Microbacterium sp. XT11. Mibgl3 shows typical structural features of the GH3 family, but has low sequence identity with other GH3 enzymes. It exhibits a wide pH range tolerance and can be activated by high concentrations of NaCI, making it commercially valuable. Mibgl3 has higher substrate specificity for oligoxanthan and can effectively hydrolyze it to release glucose and glucuronate. This knowledge of Mibgl3's enzymatic properties and hydrolysis mechanism will be beneficial for future applications.