Comparison of protein structure in crystals and in solution by laser Raman scattering. I. Lysozyme

The laser Raman-scattering technique was employed to examine the question of whether the structure of a globular protein is the same in crystals as in solution. Lysozyme was selected as a model system for this study. In the amide I and amide III regions we found a good agreement between the Raman spectra of lysozyme chloride crystals (in 100% relative humidity) and lysozyme solution (at pH 4.50), indicating that the main-chain conformation is the same between two phases. However, small but definite spectral differences were observed near 464, 622, 644, 934, 960, 978, 1032, 1129, and 1196 cm^-1. Some of these spectral differences may be interpreted in terms of side-chain conformational changes. Additionally, we present Raman spectrum of lysozyme in the lyophilized form and compare it to those of crystals and solution. It was concluded that lyophilization caused conformational changes appreciably, both in the main chain and side chain.