Interactions of lens proteins. Concentration dependence of β-crystallin aggregation

The concentration-dependence of β-crystallin aggregation was studied by both high- and low-pressure size exclusion chromatography of calf lens cortical extract (0·5–249 mg ml −1), nuclear extract (0·2–304 mg ml −1) and purified β-crystallins (0·4–52 mg ml −1). A reversible equilibrium exists between β H(igh)-crystallins (predominantly hexamers) and a portion of the β L(ow)-crystallins (predominantly dimers). Association to β H-crystallin is more extensive in the nucleus than in the cortex. Moreover, at physiological protein concentrations, the weight percentage of β H-crystallins is greater than that of β L-crystallins, in both the cortex and the nucleus. β H-Crystallins can be fully dissociated to β L-crystallin at low protein concentration. On the other hand, not all of the β L species are competent to associate to β H at high concentrations. This association appears to be directly dependent on the presence of βB 1 chains. We therefore propose that the concentration and spatial distribution of β H-crystallin in vivo is actually regulated by differential synthesis of βB 1 polypeptides.