A HYDROPHOBIC INTERACTION SITE FOR LYSOZYME BINDING TO POLYETHYLENE-GLYCOL AND MODEL CONTACT-LENS POLYMERS

Proton nuclear magnetic resonance (H-1-NMR) spectroscopy is used to id entify a preferred binding site for uncharged hydrophilic polymers on the surface of hen egg-white lysozyme. Chemical shift titrations show that exchangeable proton signals from amino acids Arg-61, Trp-62, Trp- 63, Arg-73, Lys-96 and Asp-101 are selectively perturbed upon binding of poly(ethylene oxide), poly(ethylene glycol) and poly(ethylene-co-pr opylene oxide). The greatest binding-induced chemical shift changes ar e observed for Trp-62, Arg-61 and Arg-73 at the edge of the active sit e cleft of the protein, consistent with a predominantly hydrophobic in teraction mode involving the polymer ethylene moieties. The more hydro philic species poly(dihydroxypropyl methacrylate) causes similar but s ubstantially smaller chemical shift effects than the other polymers, c onfirming the nature of the interaction. A dissociation constant of 76 +/- 5 mM is determined for the poly(ethylene glycol)-lysozyme complex . The relatively low affinity of the protein-polymer interactions comp ared to oligosaccharide substrate binding suggests that lysozyme activ ity is minimally affected by these materials. (C) 1998 Published by El sevier Science Ltd. All rights reserved