In vitro and in silico analyses reveal the interaction between LysM receptor-like kinase3 of Solanum tuberosum and the carbohydrate elicitor Riclin octaose

As a carbohydrate elicitor, Riclin octaose (Rioc) activates the pattern-triggered immunity of Solanum tuberosum L., while how the plant perceives Rioc is unknown. Here, a pattern recognition receptor StLYK3 (LysM receptor-like kinase3) whose transcription level was significantly up-regulated after Rioc elicitation was investigated in vitro and in silico. The nucleotide that encoded the ectodomain of StLYK3 (StLYK3-ECD) was heterologously expressed in the Pichia pastoris strain GS115. The purified StLYK3-ECD had the molecular weight of 25.08 kDa and pI of 5.69. Afterwards interaction between StLYK3-ECD and Rioc was analyzed by isothermal titration calorimetry. The molar ratio of ligand to receptor, dissociation constant, and enthalpy were 1.28 +/- 0.04, 26.7 +/- 3.1 mu M, and -45.0 +/- 1.8 kJ mol(-1), respectively. Besides, molecular dynamics results indicated that StLYK3-ECD contained three carbohydrate-binding motifs and the first two motifs probably contributed to the interaction with Rioc via hydrogen bond and van de Waals' forces. Amino acids containing hydroxyl, amidic, and sulfhydryl groups took the main portion in the docking site. Moreover, replacing the 92nd threonyl (T) of StLYK3-ECD with valyl (V) resulted in the alteration of the preferred docking site. The dissociation constant drastically increased to 841.6 +/- 232.4 mu M. In conclusion, StLYK3 was a potential receptor of Rioc.