Structural Changes in α-Crystallin and Whole Eye Lens During Heating, Observed by Low-angle X-ray Diffraction

Whole eye lens and α-crystallin gels and solutions were investigated using X-ray scattering techniques at temperatures ranging from 20 °C to 70 °C. In whole lens isolated in phosphate-buffered saline, the spacing of the dominant X-ray reflection seen with low-angle scattering was constant from 20 °C to 45 °C but increased at 50 °C from 15.2 nm to 16.5 nm. At room temperature, the small-angle X-ray diffraction pattern of the intact lens was very similar to the pattern of α-crystallin gels at near-physiological concentration (≈300 mg/ml), so it is reasonable to assume that the α-crystallin pattern dominates the pattern of the intact lens. Our results therefore indicate that in whole lens α-crystallin is capable of maintaining its structural properties over a wide range of temperature. This property would be useful in providing protection for other lens proteins super-aggregating. In the α-crystallin gels, a moderate increase in both the spacing and intensity of the reflection was observed from 20 °C to 45 °C, followed by an accelerated increase from 45 °C to 70 °C. Upon cooling, this effect was found to be irreversible over 11 hours. Qualitatively similar results were observed for α-crystallin solutions at a variety of lower concentrations.