Primary gene products of bovine beta-crystallin and reassociation behavior of its aggregates.

Abstract

beta-Crystallin from calf lens cortex was fractionated in three different aggregates of increasing size: beta L2- beta L1 and beta H. of which the subunit composition was revealed by 2-dimensional gel electrophoresis. While beta L2 mainly consists of beta Bp (the major polypeptide chain in all three aggregates). beta L1 is characterized by the addition of a neutral and two acidic chains, and beta H contains moreover two basic chains. Translation of calf lens polyribosomes in a reticulocyte cell-free system allowed the identification of six beta-crystallin subunits as primary gene products. The distribution of these newly synthesized polypeptides over the three aggregates was established after gel filtration in the presence of carrier lens proteins. The aggregation behavior of the beta-crystallin chains was studied by dissociation reassociation experiments. The three separate aggregates could be reversibly dissociated. Reassociation of basic, neutral and acidic polypeptides, isolated by ion-exchange chromatography of beta-crystallin, produced a beta H-like aggregate. The neutral and acidic polypeptides reassociated into a beta L1-like aggregate, while the neutral polypeptides gave dimers like beta L2. A beta H-like aggregate could also be obtained by reaggregation of beta L2 with the acidic and basic chains of beta H. On the basis of these results a preliminary model for the formation of beta-crystallin aggregates is discussed.