Chitooligosaccharide binding to CIA17 (Coccinia indica agglutinin). Thermodynamic characterization and formation of higher order complexes

• Published in: International journal of biological macromolecules Vol. 137; pp. 774 - 782
• Main Authors: Bobbili, Kishore Babu, Singh, Bipin, Narahari, Akkaladevi, Bulusu, Gopalakrishnan, Surolia, A., Swamy, Musti J.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.09.2019
• Subjects: Acetylation; Chitosan - chemistry; Isothermal titration calorimetry; Molecular Docking Simulation; Molecular Dynamics Simulation; Molecular dynamics simulations; Oligosaccharides - chemistry; Oligosaccharides - metabolism; Phloem protein 2; Plant Lectins - chemistry; Plant Lectins - metabolism; Protein Conformation; Thermodynamics; Phloem protein 2; Isothermal titration calorimetry; Molecular dynamics simulations
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2019.06.211

CIA17 is a PP2-like, homodimeric lectin made up of 17 kDa subunits present in the phloem exudate of ivy gourd (Coccinia indica). Isothermal titration calorimetric (ITC) studies on the interaction of chitooligosaccharides [(GlcNAc)2–6] showed that the dimeric protein has two sugar binding sites which recognize chitotriose with ~70-fold higher affinity than chitobiose, indicating that the binding site is extended in nature. ITC, atomic force microscopic and non-denaturing gel electrophoresis studies revealed that the high-affinity interaction of CIA17 with chitohexaose (Ka = 1.8 × 107 M−1) promotes the formation of protein oligomers. Computational studies involving homology modeling, molecular docking and molecular dynamics simulations on the binding of chitooligosaccharides to CIA17 showed that the protein binding pocket accommodates up to three GlcNAc residues. Interestingly, docking studies with chitohexaose indicated that its two triose units could interact with binding sites on two protein molecules to yield dimeric complexes of the type CIA17-(GlcNAc)6-CIA17, which can extend in length by the binding of additional chitohexaose and CIA17 molecules. These results suggest that PP2 proteins play a role in plant defense against insect/pathogen attack by directly binding with the higher chain length chitooligosaccharides and forming extended, filamentous structures, which facilitate wound sealing. [Display omitted] •CIA17 is a PP2 family phloem exudate lectin which recognizes chitooligosaccharides•ITC studies show that CIA17 exhibits 70-fold higher affinity for chitotriose than chitobiose•ITC and AFM studies show that CIA17-chitohexaose interaction leads to the formation of protein oligomers•Modeling studies showed that two triose units of chitohexaose simultaneously interact with two CIA17 molecules•Interaction of CIA17 and longer chitooligosaccharides yields filamentous structures, which facilitate wound sealing