D-amino acid formation induced by a chiral field within a human lens protein during aging

Biochem Biophys Res Commun. 1999 Sep 24;263(2):322-6. doi: 10.1006/bbrc.1999.1279.

Abstract

We have previously shown that Asp-151 in alphaA-crystallin from aged human lens are converted to the biologically uncommon D-isomer to a high degree, showing that the formation of D-isomer was not simple racemization, but stereoinvertion. This suggests that alphaA-crystallin has a chiral reaction field which promotes the inversion of L-Asp to D-Asp residues in the native higher order structure of alphaA-crystallin itself. Here, we show that when the aged human alphaA-crystallin, enriched at Asp-151 with the D-isomer (D/L ratio of 5.7), was unfolded by heating at 70 degrees C or 6 M urea, the D-Asp-151 in the unfolded alphaA-crystallin was rapidly racemized (D/L ratio of 2.17 to 1.21). This presumably reflects a relaxation of the chiral field that was initially inducing the stereoinversion from the natural L-isomer to the D-isomer.

MeSH terms

  • Aged
  • Aged, 80 and over
  • Aging / physiology*
  • Aspartic Acid / chemistry*
  • Crystallins / chemistry*
  • Humans
  • Lens, Crystalline / chemistry*
  • Models, Chemical
  • Oligopeptides / chemistry
  • Peptide Fragments / chemistry
  • Protein Conformation
  • Protein Denaturation
  • Sequence Analysis
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
  • Stereoisomerism

Substances

  • Crystallins
  • Oligopeptides
  • Peptide Fragments
  • Aspartic Acid