A DYNAMIC QUATERNARY STRUCTURE OF BOVINE ALPHA-CRYSTALLIN AS INDICATED FROM INTERMOLECULAR EXCHANGE OF SUBUNITS

The structural bovine eye lens protein α-crystallin was dissociated in 7 M urea and its four subunits, A1 A2, B1 and B2, were separated by means of ion-exchange chromatography. Homopolymeric reaggregates of these subunits were prepared by removal of the denaturant via dialysis. It was found that subunits were exchanged upon incubation of mixtures of two homopolymers under native conditions. New hybrid species were formed within 24 h as demonstrated by isoelectric focusing. Moreover, native α-crystallin molecules also exchanged subunits when incubated with homopolymeric aggregates of B2 subunits. Subunit exchange between native α-crystallin molecules is postulated, and a “dynamic quaternary structure” is presented that allows the polydisperse protein to adapt to changes in cytoplasmic conditions upon aging of the lens tissue. © 1990, American Chemical Society. All rights reserved.