QUATERNARY INTERACTIONS IN EYE LENS BETA-CRYSTALLINS - BASIC AND ACIDIC SUBUNITS OF BETA-CRYSTALLINS FAVOR HETEROLOGOUS ASSOCIATION

β-Crystallins are complex eye lens proteins made up of several related basic and acidic subunits that combine to form differently sized oligomers each displaying extensive polydispersity. As the sequences are homologous to the X-ray-determined bilobal structure of γ-crystallin, β-subunits are visualized as having a similar structure with additional N- and C-terminal extensions. Two basic (βB2 and βB3) and two acidic (βA3 and βA4) subunits have been isolated in deaggregating media, refolded, and reassociated in various combinations to determine which components favor dimers or higher oligomers. Homopolymers were compared with βB2 homodimer in terms of charge, using Mono Q fast protein liquid chromatography, and size, using Superose 12 chromatography. Heterooligomeric formations were monitored by their intermediate charge properties compared with homooligomers. βB2 associates with either βB3- or βA4-forming heterodimers whereas a larger oligomer is formed with βA3. Naturally occurring β-crystallin oligomers were analyzed by Mono Q chromatography and PhastGel electrophoresis. Whereas βB2, βB3, and βA4 can each be reassociated to homodimers, βA4 dimers are not found in native β-crystallins. βB2-βA3 is a major component of intermediate-sized βL1crystallin and is absent from dimeric βL2-crystallin. It is suggested that the pH dependence of the size of βL1crystallin is due to a dimer to tetramer equilibrium. By following dimer interactions using Superose 12 chromatography, βB2-βA4 was shown to interact with βB2-βA3. A model of β-crystallin structure is proposed based on β-subunits forming dimers with the next level of organization requiring an acidic subunit, βA3, with a long N-terminal extension. © 1990, American Chemical Society. All rights reserved.