The calf gamma crystallins--a Raman spectroscopic study

The solution structures of the four major components of bovine lens gamma-crystallin, gamma s, gamma II, gamma III and gamma 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 (1,000-1,700 cm-1) are strikingly similar in all four gamma-crystallin fractions. These similarities are indicative of the dominant anti-parallel beta sheet structure common to all the gamma-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 gamma-crystallin fractions are moderately hydrogen bonded. Distinct differences in the solution structures of the gamma-crystallins were observed in the higher energy end of the vibrational Raman spectra. The sulfhydryl stretching frequencies for the gamma-crystallins exhibit complex splitting patterns in the 2,500-2,600 cm-1 region. These patterns are due to the competing effects of hydrogen bonding and S-pi 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.