Multifunctional lens crystallins and corneal enzymes. More than meets the eye

Ann N Y Acad Sci. 1998 Apr 15;842:7-15. doi: 10.1111/j.1749-6632.1998.tb09626.x.


The abundant water-soluble proteins, called crystallins, of the transparent, refractive eye lens have been recruited from metabolic enzymes and stress-protective proteins by a process called "gene sharing." Many crystallins are also present at lower concentration in nonocular tissues where they have nonrefractive roles. The complex expression pattern of the mouse alpha B-crystallin/small heat shock protein gene is developmentally controlled at the transcriptional level by a combinatorial use of shared and lens-specific regulatory elements. A number of crystallin genes, including that for alpha B-crystallin, are activated by Pax-6, a conserved transcription factor for eye evolution. Aldehyde dehydrogenase class 3 and transketolase are metabolic enzymes comprising extremely high proportions of the water-soluble proteins of the cornea and may have structural as well as enzymatic roles, reminiscent of lens enzyme-crystallins. Inductive processes appear to be important for the corneal-preferred expression of these enzymes. The use of the same protein for entirely different functions by a gene-sharing mechanism may be a general strategy based on evolutionary tinkering at the level of gene regulation.

Publication types

  • Review

MeSH terms

  • Animals
  • Cornea / enzymology*
  • Cornea / physiology
  • Crystallins / genetics
  • Crystallins / physiology*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / physiology
  • Evolution, Molecular
  • Eye Proteins / genetics
  • Eye Proteins / physiology
  • Gene Expression Regulation
  • Heat-Shock Proteins / genetics
  • Homeodomain Proteins*
  • Humans
  • PAX6 Transcription Factor
  • Paired Box Transcription Factors
  • Repressor Proteins
  • Solubility


  • Crystallins
  • DNA-Binding Proteins
  • Eye Proteins
  • Heat-Shock Proteins
  • Homeodomain Proteins
  • PAX6 Transcription Factor
  • PAX6 protein, human
  • Paired Box Transcription Factors
  • Pax6 protein, mouse
  • Repressor Proteins