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

Xanthan: enzymatic degradation and novel perspectives of applications

The extracellular heteropolysaccharide xanthan, synthesized by bacteria of the genus Xanthomonas, is widely used as a thickening and stabilizing agent across the food, cosmetic, and pharmaceutical sectors. Expanding the scope of its application, current efforts target the use of xanthan to develop innovative functional materials and products, such as edible films, eco-friendly oil surfactants, and biocompatible composites for tissue engineering. Xanthan-derived oligosaccharides are useful as nutritional supplements and plant defense elicitors. Development and processing of such new functional materials and products often necessitate tuning of xanthan properties through targeted structural modification. This task can be effectively carried out with the help of xanthan-specific enzymes. However, the complex molecular structure and intricate conformational behavior of xanthan create problems with its enzymatic hydrolysis or modification. This review summarizes and analyzes data concerning xanthan-degrading enzymes originating from microorganisms and microbial consortia, with a particular focus on the dependence of enzymatic activity on the structure and conformation of xanthan. Through a comparative study of xanthan-degrading pathways found within various bacterial classes, different microbial enzyme systems for xanthan utilization have been identified. The characterization of these new enzymes opens new perspectives for modifying xanthan structure and developing innovative xanthan-based applications. KEY POINTS: • The structure and conformation of xanthan affect enzymatic degradation. • Microorganisms use diverse multienzyme systems for xanthan degradation. • Xanthan-specific enzymes can be used to develop xanthan variants for novel applications.

An Insight into the Essential Role of Carbohydrate-Binding Modules in Enzymolysis of Xanthan

To date, due to the low accessibility of enzymes to xanthan substrates, the enzymolysis of xanthan remains deficient, which hinders the industrial production of functional oligoxanthan. To enhance the enzymatic affinity against xanthan, the essential role of two carbohydrate binding modules—MiCBMx and PspCBM84, respectively, derived from Microbacterium sp. XT11 and Paenibacillus sp. 62047—in catalytic properties of endotype xanthanase MiXen were investigated for the first time. Basic characterizations and kinetic parameters of different recombinants revealed that, compared with MiCBMx, PspCBM84 dramatically increased the thermostability of endotype xanthanase, and endowed the enzyme with higher substrate affinity and catalytic efficiency. Notably, the activity of endotype xanthanase was increased by 16 times after being fused with PspCBM84. In addition, the presence of both CBMs obviously enabled endotype xanthanase to produce more oligoxanthan, and xanthan digests prepared by MiXen-CBM84 showed better antioxidant activity due to the higher content of active oligosaccharides. The results of this work lay a foundation for the rational design of endotype xanthanase and the industrial production of oligoxanthan in the future.