Triose phosphate isomerase, a novel enzyme-crystallin, and τ-crystallin in crocodile cornea: High accumulation of both proteins during late embryonic development

Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad-500 007, India.
FEBS Journal (Impact Factor: 4). 08/2006; 273(14):3370-80. DOI: 10.1111/j.1742-4658.2006.05344.x
Source: PubMed


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 tau-crystallin/alpha-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. tau-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 tau-crystallin and TIM are concentrated largely in the corneal epithelium. Using western blot, immunofluorescence and enzymatic activity, we demonstrate that high accumulation of tau-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 alpha-enolase and TIM activities, which increases in the corneal extract with development. Our results establishing the presence of tau-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.

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Available from: Krishnakumar Vaithilingam,
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    • "However, it has been noted that it shows close phylogenetic resemblance to some crystallin enzymes, in particular those found in mammals. These proteins and enzymes are primarily known for their role in lens and cornea structure and transparency [48,49]. However, their malfunctioning has been linked to a number of diseases including cataract formation and cancer. "
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    • "Well defined examples of corneal crystallins include glutathione-S-transferase (GST)/Ω-crystallin [6], aldehyde dehydrogenase (ALDH) 3Aβ [7], ALDH1A1/η-crystallin [3,8], α-enolase/τ-crystallin [6,9], arginino-succinate lyase/δ-crystalllin [6], lactate dehydrogenase (LDH)/ε-crystallin [10], transketolase (TKT) [11], and gelsolin [12]. The list continues to grow, to which GAPDH/π-crystallin [13], triose phosphate isomerase (Tpi) [9], and scinderin-like gene [14] were added in recent years. "
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    • "Since the corneal epithelium and the lens are both derived from ectoderm, it seems reasonable to propose that the evolution of transparency in these two structures may have co-evolved as an integrated 'refracton' unit. Indeed, data showing that the corneas from a diverse range of species including squid, fish, frogs, crocodiles, birds and mammals abundantly express a few water-soluble proteins is consistent with this theory [6] [7] [9] [10] [11] [13]. However, the vast majority of studies identifying corneal crystallin expression have used total corneal extracts or isolated corneal epithelium. "
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