Oligomerization and conformation change in solutions of calf lens gamma II-crystallin. Results from 1/T1 nuclear magnetic relaxation dispersion profiles

Abstract

From analyses of the magnetic field dependence of 1/T1 (nuclear magnetic relaxation dispersion [NMRD] profiles) of water protons in solutions of highly purified calf lens gamma II-crystallin, we find that monomers form oligomers at relatively low concentrations, which increase in size with increasing concentration and decreasing temperature. At approximately 16% by volume and -4 degrees C, the mean oligomeric molecular weight is approximately 120-fold greater than the monomeric value of 20 kD. Below this concentration, there is no indication of any substantive change in conformation of the monomeric subunits. At higher concentrations, the tertiary structure of the monomer appears to reconfigure rather abruptly, but reversibly, as evidenced by the appearance of spectra-like 14N peaks in the NMRD profiles. The magnitudes of these peaks, known to arise from cross-relaxation of water protons through access to amide (NH) moieties of the protein backbone, indicate that the high concentration conformation is not compact, but open and extended in a manner that allows enhanced interaction with solvent. The data are analogous to those found for homogenates of calf and chicken lens (Beaulieu, C. F., J. I. Clark, R. D. Brown III, M. Spiller, and S. H. Koenig. 1988. Magn. Reson. Med. 8:47-57; Beaulieu, C. F., R. D. Brown III, J. I. Clark, M. Spiller, and S. H. Koenig. 1989. Magn. Reson. Med. 10:62-72). This unusually large dependence of oligomeric size and conformation on concentration in the physiological range is suggested as the mechanism by which osmotic equilibrium is maintained, at minimal metabolic expense, in the presence of large gradients of protein concentration in the lens in vivo (cf Vérétout and Tardieu, 1989. Eur. Biophys. J. 17:61-68). Finally, the results of the NMRD data provide a ready explanation of the low temperature phase transition, and "cold-cataract" separation of phases, observed in gamma II-crystallin solutions; we suggest that the phases that separate are the two major conformers detected by NMRD.

A Small‐Angle Neutron Scattering Study of γ‐Crystallins Near Their Isoelectric Point

“…We can conclude that there is a temperature-induced aggregation or temporal associations but we cannot quantify them. Recently, Koenig et al found that 7-crystallin fractions aggregate as the temperature decreases (Koenig et a]., 1990(Koenig et a]., , 1992. They claim that the phase transition observed in y-crystallin solutions is driven by the formation of these protein aggregates.…”

Protein Self-Association in Solution: The Bovine Pancreatic Trypsin Inhibitor Decamer

“…Here, we use 1 H MRD to determine the rotational correlation times (or rotational diffusion coefficients) of the oligomeric species present in solution. Whereas MRD has been used in a few earlier studies of protein selfassociation (Lindstrom et al, 1976;Raeymaekers et al, 1989;Koenig et al, 1990), our data extend to higher frequencies (necessary for a small protein like BPTI) and are analyzed in a more rigorous way (Halle et al, 1998).…”