Triose phosphate isomerase, a novel enzyme-crystallin, and τ-crystallin in crocodile cornea

Abstract

Several enzymes are known to accumulate in the cornea in unusually high concentrations. Based on the analogy with lens crystallins, these enzymes are called corneal crystallins, which are diverse and species-specific. Examining crystallins in lens and cornea in multiple species provides great insight into their evolution. We report data on major proteins present in the crocodile cornea, an evolutionarily distant taxon. We demonstrate that τ-crystallin/α-enolase and triose phosphate isomerase (TIM) are among the major proteins expressed in the crocodile cornea as resolved by 2D gel electrophoresis and identified by MALDI-TOF. These proteins might be classified as putative corneal crystallins. τ-Crystallin, known to be present in turtle and crocodile lens, has earlier been identified in chicken and bovine cornea, whereas TIM has not been identified in the cornea of any species. Immunostaining showed that τ-crystallin and TIM are concentrated largely in the corneal epithelium. Using western blot, immunofluorescence and enzymatic activity, we demonstrate that high accumulation of τ-crystallin and TIM starts in the late embryonic development (after the 24th stage of embryonic development) with maximum expression in a two-week posthatched animal. The crocodile corneal extract exhibits significant α-enolase and TIM activities, which increases in the corneal extract with development. Our results establishing the presence of τ-crystallin in crocodile, in conjunction with similar reports for other species, suggest that it is a widely prevalent corneal crystallin. Identification of TIM in the crocodile cornea reported here adds to the growing list of corneal crystallins.