Split Enzyme-Based Biosensors for Structural Characterization of Soluble and Insoluble β-Glucans

beta-Glucan is widely distributed in various plants and microorganisms and is composed of beta-1,3-linked D-glucose units. It may have a branched short or long side chain of glucose units with beta-1,6- or beta-1,4-linkage. Numerous studies have investigated different beta-glucans and revealed their bioactivities. To understand the structure-function relationship of beta-glucan, we constructed a split-luciferase complementation assay for the structural analysis of long-chain beta-1,6-branched beta-1,3-glucan. The N- and C-terminal fragments of luciferase from deep-sea shrimp were fused to insect-derived beta-1,3-glucan recognition protein and fungal endo-beta-1,6-glucanase (Neg1)-derived beta-1,6-glucan recognition protein, respectively. In this approach, two beta-glucan recognition proteins bound to beta-glucan molecules come into close proximity, resulting in the assembly of the full-length reporter enzyme and induction of transient luciferase activity, indicative of the structure of beta-glucan. To test the applicability of this assay, beta-glucan and two beta-glucan recognition proteins were mixed, resulting in an increase in the luminescence intensity in a beta-1,3-glucan with a long polymer of beta-1,6-glucan in a dose-dependent manner. This simple test also allows the monitoring of real-time changes in the side chain structure and serves as a convenient method to distinguish between beta-1,3-glucan and long-chain beta-1,6-branched beta-1,3-glucan in various soluble and insoluble beta-glucans.

Automated summary

Beta-glucan, consisting of beta-1,3-linked D-glucose units, is present in various plants and microorganisms with diverse structures and bioactivities. A split-luciferase complementation assay was developed for the structural analysis of long-chain beta-1,6-branched beta-1,3-glucan, demonstrating the potential for real-time monitoring and differentiation of beta-glucans.