Eye lens alphaA- and alphaB-crystallin: complex stability versus chaperone-like activity.
The major lens protein alpha-crystallin is composed of two related types of subunits, alphaA- and alphaB-crystallin, of which the former is essentially lens-restricted, while the latter also occurs in various other tissues. With regard to their respective chaperone capacities, it has been reported that homomultimeric alphaA-crystallin complexes perform better in preventing thermal aggregation of proteins, while alphaB-crystallin complexes protect more efficiently against reduction-induced aggregation of proteins. Here, we demonstrate that this seeming discrepancy is solved when the reduction assay is performed at increasing temperatures: above 50 degrees C alphaA- performs better than alphaB-crystallin also in this assay. This inversion in protective capacity might relate to the greater resistance of alphaA-crystallin to heat denaturation. Infrared spectroscopy, however, revealed that this is not due to a higher thermostability of alphaA-crystallin's secondary structure. Also the accessible hydrophobic surfaces do not account for the chaperoning differences of alphaA- and alphaB-crystallin, since regardless of the experimental temperature alphaB-crystallin displays a higher hydrophobicity. It is argued that the greater complex stability of alphaA-crystallin, as evident upon urea denaturation, and the higher chaperone capacity of alphaB-crystallin at physiological temperatures reflect the evolutionary compromise to obtain an optimal functioning of heteromeric alpha-crystallin as a lens protein.
van Boekel
M A
MA
Department of Biochemistry, University of Nijmegen, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands. m.vanboekel@bioch.kun.nl
de Lange
F
F
de Grip
W J
WJ
de Jong
W W
WW
D000817:Anilino Naphthalenesulfonates; D000818:Animals; D002417:Cattle; D011232:Chemical Precipitation; D002850:Chromatography, Gel; D003459:Crystallins / Q000737:chemistry*; D005456:Fluorescent Dyes; D007328:Insulin / Q000737:chemistry; D018832:Molecular Chaperones / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D014508:Urea
D000817:Anilino Naphthalenesulfonates; D003459:Crystallins; D005456:Fluorescent Dyes; D007328:Insulin; D018832:Molecular Chaperones; D011994:Recombinant Proteins; C027132:1-anilino-8-naphthalenesulfonate; D014508:Urea