We determined the crystal structure of a LysM module from Pteris ryukyuensis chitinase-A (PrLysM2) at a resolution of 1.8 angstrom. 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 (Delta G(r)degrees) for binding of (GIcNAc)(6), (G1cNAc)(5), and (GIcNAc)(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 (GIcNAc)(6) revealed that the driving force is the enthalpy change (Delta H-r degrees = -11.7 +/- 0.2 kcal/mol) and the solvation entropy change (-T Delta S-solv degrees = -5.9 +/- 0.6 kcal/mol). This is the first description of thermodynamic signatures of a chitin oligosaccharide binding to a LysM module. (C) 2017 Elsevier Inc. All rights reserved.