Identification of a cytosolic NADP+-dependent isocitrate dehydrogenase that is preferentially expressed in bovine corneal epithelium. A corneal epithelial crystallin

J Biol Chem. 1999 Jun 11;274(24):17334-41. doi: 10.1074/jbc.274.24.17334.


Recently, metabolic enzymes have been observed in both the lens and corneal epithelium at levels greatly exceeding what is necessary for normal metabolic functions. These proteins have been termed taxon-specific crystallins and are thought to play a role in maintaining tissue transparency. We report here that cytosolic NADP+-dependent isocitrate dehydrogenase (ICDH) represents a new corneal crystallin. Using suppression subtractive hybridization, we identified a gene (with a deduced amino acid sequence that showed 94% identity to rat cytosolic NADP+-dependent ICDH) that is preferentially expressed in bovine corneal epithelium. Northern blots established that its mRNA level in the corneal epithelium was 31-, 39-, 133-, 230-, and 929-fold more than in the liver, bladder epithelium, stomach epithelium, brain, and heart, respectively. This mRNA was detected primarily in corneal epithelial basal cells by in situ hybridization. SDS-polyacrylamide gel electrophoresis, two-dimensional gel analysis, and Western blotting showed that this protein was overexpressed in the corneal epithelium, constituting approximately 13% of the total soluble bovine corneal epithelial proteins. Enzyme assays showed a corresponding overabundance of this protein in bovine corneal epithelium. Taken together, these data indicate that bovine cytosolic ICDH fulfills the criteria for a corneal epithelial crystallin and may be involved in maintaining corneal epithelial transparency.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Cattle
  • Cell Compartmentation
  • Crystallins / genetics*
  • Crystallins / isolation & purification
  • Cytosol / enzymology*
  • DNA, Complementary / genetics
  • Epithelium, Corneal / enzymology*
  • Gene Library
  • Humans
  • In Situ Hybridization
  • Isocitrate Dehydrogenase / genetics*
  • Isocitrate Dehydrogenase / isolation & purification
  • Mice
  • Molecular Sequence Data
  • Rabbits
  • Rats
  • Sequence Analysis, DNA
  • Sequence Homology, Amino Acid
  • Species Specificity
  • Tissue Distribution


  • Crystallins
  • DNA, Complementary
  • Isocitrate Dehydrogenase
  • isocitrate dehydrogenase (NADP+)

Associated data

  • GENBANK/AF136009