Polarized Raman spectroscopic studies of tetragonal lysozyme single crystals

Polarized Raman spectra have been obtained for tetragonal lysozyme single c rystals of different relative quality. The Raman band at 507 cm(-1), which corresponds to the totally symmetric stretch vibration of the gauche-gauche -gauche (ggg) disulfide bridges of the protein, has been shown to possess d ifferent polarization characteristics compared with the gauche-gauche-trans (ggt) disulfide bridge band at 528 cm(-1). The relative intensities of the ggg and ggt bands in the polarized Raman spectra have been numerically est imated for a number of tetragonal lysozyme single crystals, the X-ray diffr action data of which are available from the Protein Data Bank. On the basis of comparison between the experimental and calculated polarization charact eristics of the disulfide Raman lines, the following main conclusions have been drawn. The orientation of the protein molecules correlates with the av erage orientation of their ggg disulfide bridges. This in turn can be descr ibed by the rho(ggg), value which reflects the average-orientation of the S -S bands with respect to the Z crystallographic axis and can be determined from polarized Raman spectra. Crystals of better quality are characterized by a better alignment of the protein molecules with respect to the Z axis, a smaller perturbation of the protein molecules in the crystal lattice and a somewhat higher interlattice water content.