The calf gamma crystallins-A Raman spectroscopic study

The solution structures of the four major components of bovine lens γ-crystallin, γ_s, γ_II, γ_III and γ_IV are compared using Raman spectroscopy. The spectral region sensitive to the vibrational frequencies of aromatic and sulfur containing residues and to the backbone skeletal stretching modes (500-1000 cm^-1), and that reflecting secondary structure (1000-1700 cm^-1) are strikingly similar in all four γ-crystallin fractions. These similarities are indicative of the dominant anti-parallel β sheet structure common to all the γ-crystallins. A comparison of the ratios of the Raman intensities at 850 cm^-1 and 830 cm^-1 ( I₈₅₀ I₈₃₀), an empirical measure of the degree of hydrogen bonding of phenolic hydroxyl groups, suggests that the tyrosine residues in all the γ-crystallin fractions are moderately hydrogen bonded. Distinct differences in the solution structures of the γ-crystallins were observed in the higher energy end of the vibrational Raman spectra. The sulfhydryl stretching frequencies for the γ-crystallins exhibit complex splitting patterns in the 2500-2600 cm^-1 region. These patterns are due to the competing effects of hydrogen bonding and S-π interactions with neighboring aromatic residues. All five proteins exhibit multiple, but distinct, thiol frequencies, suggesting that the microenvironments of the cysteine residues in these proteins are significantly different.