Thermodynamic stability of human lens recombinant αA- and βB- crystallins

Abstract

Lens α-crystallin is a 600-800-kDa heterogeneous oligomer protein consisting of two subunits, αA and βB. The homogeneous oligomers (αA- and βB-crystallins) have been prepared by recombinant DNA technology and shown to differ in the following biophysical/biochemical properties: hydrophobicity, chaperone-like activity, subunit exchange rate, and thermal stability. In this study, we studied their thermodynamic stability by unfolding in guanidine hydrochloride. The unfolding was probed by three spectroscopic parameters: absorbance at 235 nm, Trp fluorescence intensity at 320 nm, and far-UV circular dichroism at 223 nm. Global analysis indicated that a three-state model better describes the unfolding behavior than a two- state model, an indication that there are stable intermediates for both αA- and βB-crystallins. In terms of standard free energy (ΔG(NU)(H2O)), αA- crystallin is slightly more stable than αB-crystallin. The significance of the intermediates may be related to the functioning of α-crystallins as chaperone-like molecules.