Effect of dicarbonyl-induced browning on alpha-crystallin chaperone-like activity: physiological significance and caveats of in vitro aggregation assays

Biochem J. 2004 Apr 15;379(Pt 2):273-82. doi: 10.1042/BJ20031633.

Abstract

Alpha-crystallin is a member of the small heat-shock protein family and functions like a molecular chaperone, and may thus help in maintaining the transparency of the eye lens by protecting the lens proteins from various stress conditions. Non-enzymic glycation of long-lived proteins has been implicated in several age- and diabetes-related complications, including cataract. Dicarbonyl compounds such as methylglyoxal and glyoxal have been identified as the predominant source for the formation of advanced glycation end-products in various tissues including the lens. We have investigated the effect of non-enzymic browning of alpha-crystallin by reactive dicarbonyls on its molecular chaperone-like function. Non-enzymic browning of bovine alpha-crystallin in vitro caused, along with altered secondary and tertiary structures, cross-linking and high-molecular-mass aggregation. Notwithstanding these structural changes, methylglyoxal- and glyoxal-modified alpha-crystallin showed enhanced anti-aggregation activity in various in vitro aggregation assays. Paradoxically, increased chaperone-like activity of modified alpha-crystallin was not associated with increased surface hydrophobicity and rather showed less 8-anilinonaphthalene-l-sulphonic acid binding. In contrast, the chaperone-like function of modified alpha-crystallin was found to be reduced in assays that monitor the prevention of enzyme inactivation by UV-B and heat. Moreover, incubation of bovine lens with methylglyoxal in organ culture resulted in cataract formation with accumulation of advanced glycation end-products and recovery of alpha-crystallin in high proportions in the insoluble fraction. Furthermore, soluble alpha-crystallin from methylglyoxal-treated lenses showed decreased chaperone-like activity. Thus, in addition to describing the effects of methylglyoxal and glyoxal on structure and chaperone-like activity, our studies also bring out an important caveat of aggregation assays in the context of the chaperone function of alpha-crystallin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cattle
  • Glycation End Products, Advanced / biosynthesis
  • Glycation End Products, Advanced / chemistry
  • Glyoxal / pharmacology*
  • Hydrophobic and Hydrophilic Interactions
  • Lens, Crystalline / anatomy & histology
  • Lens, Crystalline / drug effects
  • Maillard Reaction
  • Organ Culture Techniques
  • Protein Conformation
  • Protein Subunits / chemistry
  • Pyruvaldehyde / pharmacology
  • alpha-Crystallins / chemistry*
  • alpha-Crystallins / drug effects
  • alpha-Crystallins / metabolism*

Substances

  • Glycation End Products, Advanced
  • Protein Subunits
  • alpha-Crystallins
  • Glyoxal
  • Pyruvaldehyde