Influence of the C-terminal residues on oligomerization of alpha A-crystallin

Biochemistry. 2003 Oct 14;42(40):11857-63. doi: 10.1021/bi030129w.


Earlier studies have shown that the chaperone activity of alpha-crystallin is significantly affected in diabetic rat and human lenses. Subsequently, mass spectrometric analysis showed diabetic lenses having high levels of the alphaA-crystallins in which different numbers of C-terminal residues were deleted. The present study was aimed to show whether cleavage of these residues influences protein structure, oligomerization, and chaperone function. For generation of various mutants, a stop codon was introduced at the positions of interest, proteins were expressed in BL21(DE3)pLys S E. coli, and the truncated alphaA-crystallins were purified by size-exclusion chromatography. The molecular masses, as determined by molecular sieve HPLC, of mutants with deletions of 1, 5, and 10 C-terminal residues (group-1) were 519-602 kDa, and those of mutants with deletions of 11, 16, and 22 C-terminal residues (group-2) were 148-152 kDa, as compared to 607 kDa for alphaA-wild type. On the basis of circular dichroism measurements, the alpha helix content was 2-fold higher and the tertiary structure was significantly altered in the group-2 mutants. Chaperoning abilities, as determined by the ADH assay and the betaL-crystallin heat denaturation assay, of the group-1 mutants, with the exception of alphaA(1-163), were slightly improved or unchanged, that of alphaA(1-163) was moderately affected, and those of the group-2 mutants were severely affected. Most strikingly, cleavage of 11 C-terminal residues including Arg-163 showed a substantial decrease in oligomeric size and chaperone function and significant changes in protein structure whereas cleavage of 10 residues had either a small effect or no effect at all. This points to an important role for the C-terminal extension, Arg-163 in particular, and no significant role for the C-terminal flexible tail in the oligomer assembly of alphaA-crystallin.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Humans
  • Light
  • Molecular Chaperones / chemistry
  • Molecular Chaperones / genetics
  • Molecular Chaperones / metabolism
  • Molecular Weight
  • Mutagenesis, Site-Directed
  • Peptide Fragments / chemistry*
  • Protein Conformation
  • Protein Denaturation / genetics
  • Protein Structure, Tertiary
  • Rats
  • Scattering, Radiation
  • Sequence Deletion
  • Temperature
  • Thermodynamics
  • alpha-Crystallin A Chain / chemistry*
  • alpha-Crystallin A Chain / genetics
  • alpha-Crystallin A Chain / metabolism*


  • Molecular Chaperones
  • Peptide Fragments
  • alpha-Crystallin A Chain