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

The concentration-dependence of beta-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 beta-crystallins (0.4-52 mg ml-1). A reversible equilibrium exists between beta H(igh)-crystallins (predominantly hexamers) and a portion of the beta L(ow)-crystallins (predominantly dimers). Association to beta H-crystallin is more extensive in the nucleus than in the cortex. Moreover, at physiological protein concentrations, the weight percentage of beta H-crystallins is greater than that of beta L-crystallins, in both the cortex and the nucleus. beta H-Crystallins can be fully dissociated to beta L-crystallin at low protein concentration. On the other hand, not all of the beta L species are competent to associate to beta H at high concentrations. This association appears to be directly dependent on the presence of beta B1 chains. We therefore propose that the concentration and spatial distribution of beta H-crystallin in vivo is actually regulated by differential synthesis of beta B1 polypeptides.