Probing the colloidal behavior of a cell wall polysaccharides-degrading enzyme in a highly constrained model system

Understanding the specific interaction of cell wall polysaccharides degrading-enzymes with their substrates is of fundamental and practical interest for the fine grasp of their activity. Such interactions are difficult to unveil in real-life conditions due to the structural complexity of the plant cell wall. In this work, we present complex and highly confined model systems of cholesteric cellulose nanocrystal suspensions reaching dimensions close to those found in the plant cell wall. Cellulose-xyloglucan (XG) assemblies of various surface chemistries were studied, allowing to probe the interactions and diffusion behavior of a glucanase both in diluted dynamic conditions and in an organized and concentrated (110-140 g/L) cholesteric environment. QCM-D and synchrotron source-deep UV analyses showed that XG adsorbed in a flat and extended conformation changed the glucanase interaction with the polysaccharides from attractive to repulsive, making it prone to spontaneously migrate to regions with lower solid content. Furthermore, it strongly increased the enzyme diffusion kinetics. Our results confirm the preferential interaction of both enzyme and XG on the cellulose hydrophobic crystalline plane. This work provides new insights on the influence of the interaction of a protein with a substrate on its transport in a constrained environment.