Comparison between experimental Multiple Solvent Crystal Structures and Computational Solvent Mapping of Hen Eggwhite Lysozyme

Abstract

We are using the multiple solvent crystal structures (MSCS) method to map the binding surface of Hen Eggwhite Lysozyme. In the MSCS method organic solvent molecules serve as molecular probes of protein surface features. The structures presented here were solved to better than 1.9 angstroms resolution and include Lysozyme in 8M trimethylamine-N-oxide (TMAO), 2M urea, 80% acetone, 50% t-butanol, 80% isopropanol, 50% dimethylsulfoxide (DMSO). The backbone superposition of these structures reveals clustering of the organic solvents in the active site. In addition, structural adjustments to the various solvent environments delineate areas of plasticity within the macromolecule. The structures retain a significant portion of their first hydration shell, with the organic solvents behaving much more like “ligands” than like “solvents” in that they displace water only in areas that have evolved as binding sites. We compare our experimental results with those obtained using computational solvent mapping [Dennis et al, PNAS 99, 4290-4295 (2002)], where the known consensus binding pocket for the substrate is determined using urea, acetone, isopropanol, t-butanol, DMSO, methanol, methylene chloride, and acetonitrile.