Exploration of structural space of Cus17 lectin with glycans using molecular docking and simulation studies.

The Cus17 phloem protein, in the case of Cucumis sativus species, plays an important role in the phloem-based defense of the plant. Cus17 can bind to various carbohydrates present on insect exoskeletons or fungal cells. The recent experimental structure of chitotriose bound Cus17 elucidates the carbohydrate interacting residues of Cus17. Higher chito-oligosaccharides are also known to interact with Cus17, but the lack of experimental structure impedes our understanding of their interaction. In this study, we have employed in-silico methods to explore the binding interactions of higher chito-oligosaccharides with Cus17. Chitoheptaose forms stable interactions with canonical binding site residues Trp48 and Asp50. Smaller chito-oligosaccharides were observed to be relatively unstable at the canonical binding site of Cus17. Further, the chito-oligosaccharides were inspected for interactions with predicted ligand binding sites. We also generated different tetramers of Cus17 and docked the chito-oligosaccharides to the tetrameric Cus17. All chito-oligosaccharides were found to make persistent interactions with Cus17 tetramer. Interestingly, chitotriose shows the best binding affinity and maintains stable interactions with Cus17 tetramer upon extended simulations with the canonical site.