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First published online December 3, 2004
Journal of Experimental Biology 207, 4633-4649 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01312
Cold-stable eye lens crystallins of the Antarctic nototheniid toothfish Dissostichus mawsoni Norman
1 Department of Animal Biology, University of Illinois at Urbana-Champaign,
Urbana, Illinois, 61801, USA
2 Centre for Biophysics and Computational Biology, University of Illinois at
Urbana-Champaign, Urbana, Illinois, 61801, USA
3 Department of Chemical and Biomolecular Engineering, University of
Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA
* Author for correspondence (e-mail: c-cheng{at}uiuc.edu)
Accepted 22 September 2004
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,
/ßH, ß and 
, with 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 crystallin can protect
same-species 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 crystallin mixtures upon heating, which
supports formation of the complex as an integral part of the
chaperone process. Surprisingly, in cross-species chaperone assays, tuna
crystallins only partly protected toothfish crystallins, while
cow crystallins completely failed to protect, indicating partial and
no interaction, respectively. Toothfish was likely to
be the component that failed to interact, as the supernatant from a cow
plus toothfish incubation could chaperone cow
crystallins in a subsequent heat incubation, indicating the presence of
uncomplexed cow . This suggests that the inability of toothfish
crystallins to fully complex with tuna , and not at all with the cow
crystallins, may have its basis in adaptive changes in the protein
that relate to the extreme cold-stability of the toothfish lens.
Key words: lens crystallins, chaperone, Antarctic toothfish, Dissostichus mawsoni, bigeye tuna, cold adaptation, cold cataract, dynamic light scattering, alpha crystallin, gamma crystallin
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