Single-Molecule Imaging of Wood Xylans on Surfaces and Their Interaction with GH11 Xylanase

The knowledge of the molecular properties and arrangements of biopolymers in both solid and solution state are essential in the design of sustainable materials and biomedicine as they are decisive for mechanical strength, flexibility, and biodegradability. However, the structure of most biopolymers at charged interfaces can vary considerably, and their time-dependent visualization in liquid-state still remains challenging. In this work, we employed high-speed atomic force microscopy (HS-AFM) to visualize single xylan macromolecules from alkali-extracted birch and beechwood. On negatively charged mica surfaces, they appeared as individual macromolecules but assembled into aggregates on 3-aminopropyltriethoxysilane (APTES) surfaces (AP-mica). Hence, we further investigated the susceptibility to enzymatic degradation using an endoxylanase, which showed that the individual xylan macromolecules remained intact, while larger assemblies on AP-mica degraded over time. We demonstrate that HS-AFM is a powerful tool for understanding the molecular properties and degradation mechanisms of biopolymers. Moreover, by identifying alignment-dependent binding sites, strategies can be developed to ensure the biodegradability of composite materials by intelligent interface design.