Cold-stable eye lens crystallins of the Antarctic nototheniid toothfish Dissostichus mawsoni Norman
The eye lenses of the Antarctic nototheniid fishes that inhabit the perennially freezing Antarctic seawater are transparent at –2°C, whereas the cold-sensitive mammalian and tropical fish lenses display cold-induced cataract at 20°C and 7°C, respectively. No cold-cataract occurs in the giant Antarct...
| Published in: | Journal of Experimental Biology |
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| Main Authors: | , , , , , |
| Format: | Text |
| Language: | English |
| Published: |
Company of Biologists
2004
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| Subjects: | |
| Online Access: | http://jeb.biologists.org/cgi/content/short/207/26/4633 https://doi.org/10.1242/jeb.01312 |
| Summary: | The eye lenses of the Antarctic nototheniid fishes that inhabit the perennially freezing Antarctic seawater are transparent at –2°C, whereas the cold-sensitive mammalian and tropical fish lenses display cold-induced cataract at 20°C and 7°C, respectively. No cold-cataract occurs in the giant Antarctic toothfish Dissostichus mawsoni lens when cooled to temperatures as low as –12°C, indicating highly cold-stable lens proteins. To investigate this cold stability, we characterised the lens crystallin proteins of the Antarctic toothfish, in parallel with those of the sub-tropical bigeye tuna Thunnus obesus and the endothermic cow Bos taurus, representing three disparate thermal climes (–2°C, 18°C and 37°C, respectively). Sizing chromatography resolved their lens crystallins into three groups, α/β H , β and γ, with γ crystallins being the most abundant (>40%) lens proteins in fish, in contrast to the cow lens where they comprise only 19%. The upper thermal stability of these crystallin components correlated with the body temperature of the species. In vitro chaperone assays showed that fish α crystallin can protect same-species γ crystallins from heat denaturation, as well as lysozyme from DTT-induced unfolding, and therefore are small Heat Shock Proteins (sHSP) like their mammalian counterparts. Dynamic light scattering measured an increase in size of αγ crystallin mixtures upon heating, which supports formation of the αγ complex as an integral part of the chaperone process. Surprisingly, in cross-species chaperone assays, tuna α crystallins only partly protected toothfish γ crystallins, while cow α crystallins completely failed to protect, indicating partial and no αγ interaction, respectively. Toothfish γ was likely to be the component that failed to interact, as the supernatant from a cow α plus toothfish γ incubation could chaperone cow γ crystallins in a subsequent heat incubation, indicating the presence of uncomplexed cow α. This suggests that the inability of toothfish γ crystallins to fully complex with ... |
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