Crystal structure and thermodynamic dissection of chitin oligosaccharide binding to the LysM module of chitinase-A from Pteris ryukyuensis

We determined the crystal structure of a LysM module from Pteris ryukyuensis chitinase-A (PrLysM2) at a resolution of 1.8 A. Structural and binding analysis of PrLysM2 indicated that this module recognizes chitin oligosaccharides in a shallow groove comprised of five sugar-binding subsites on one side of the molecule. The free energy changes (ΔGr°) for binding of (GlcNAc)6, (GlcNAc)5, and (GlcNAc)4 to PrLysM2 were determined to be -5.4, -5,4 and -4.6 kcal mol-1, respectively, by ITC. Thermodynamic dissection of the binding energetics of (GlcNAc)6 revealed that the driving force is the enthalpy change (ΔHr° = -11.7 ± 0.2 kcal/mol) and the solvation entropy change (-TΔSsolv° = -5.9 ± 0.6 kcal/mol). This is the first description of thermodynamic signatures of a chitin oligosaccharide binding to a LysM module.