Construction of enzyme-substrate complexes between hen egg-white lysozyme and N-acetyl-D-glucosamine hexamer by systematic conformational search and molecular dynamics simulation.

We constructed the complexes between HEWL and (GlcNAc)6 oligomer in order to investigate the amino acid residues related to substrate binding in the productive and nonproductive complexes, and the relationship between the distortion of the GlcNAc residue D and the formation of the productive complexes. We obtained 49 HEWL-(GlcNAc)6 complexes by a systematic conformational search and classified the each one to the three binding modes; left side, center, or right side. Furthermore we performed the molecular dynamics simulation against 20 HEWL-(GlcNAc)6 complexes (8: chair model, 12 : half-chair model) selected from the 49 complexes to investigate the interaction between HEWL and (GlcNAc)6. As results, we confirmed that it is necessary for GlcNAc residue D to be half-chaired form to bind toward the right side to form productive complexes. We found newly that eight amino acid residues interact with the (GlcNAc)6 oligomer, as follows, Arg73, Gly102, Asn103 for GlcNAc residue A; Asn103 for GlcNAc residues B and C; Leu56, Ala107, Val109 for GlcNAc residue D; Ala110 for GlcNAc residue E; and Lys33 for GlcNAc residue F. We also indicated that GlcNAc residue F does not interact with Thr47 and rarely interacts with Phe34 and Asn37.