A H-1-NMR SPECTROSCOPIC COMPARISON OF GAMMA(S)-CRYSTALLIN AND GAMMA(B)-CRYSTALLIN

Two-dimensional H-1 NMR spectroscopic studies are presented on bovine gamma(S)- and gamma(B)-crystallin. In gamma(S)- crystallin, the four N-terminal residues have great flexibility compared with the rest of the molecule and assume a random coil conformation. NMR spectroscopy and electrospray mass spectrometry show that the N-terminal residue is acetylated. Thus, gamma(S)-crystallin is similar to the acidic beta-crystallins in having a flexible N-terminal extension and an N-terminus that is blocked with an acetyl group but no C-terminal extension. In addition to the short N-terminal extension in gamma(S)-crystallin, other unassigned resonances are also observed in the NMR spectra. In gamma(B)-crystallin, however, cross-peaks in the NH to alpha-CH region of the spectrum are essentially restricted to the last three residues of the C-terminal domain. The NMR data imply that gamma(S)-crystallin has a more flexible structure than gamma(B)-crystallin. Sedimentation equilibrium studies on gamma(S)-crystallin are consistent with this proposal. Resonances from the N-terminal extension of gamma(S)-crystallin are not affected by the presence of alpha-crystallin implying that this region is not involved in interactions between the two molecules. It is concluded that gamma,-crystallin shares structural properties which are intermediate between the beta- and gamma-crystallins.