At subzero temperatures, many animals would discover that their eye lenses go cloudy as they develop cold-induced cataracts. But the giant Antarctic toothfish has no problems seeing, despite living in permanently freezing Antarctic seas. To investigate the incredible cold stability of Antarctic toothfish eye lens proteins, Andor Kiss, Art DeVries and Chi-Hing Cheng at the University of Illinois decided to compare lens crystallin proteins from Antarctic toothfish, warm-water fish and cows(p. 4633). They hoped that studying lenses from three different thermal environments would shed light on the relationship between lens protein cold-stability and body temperature over evolutionary timescales.
The team already knew that eye lenses contain three classes of protein:α, β and γ crystallins. Mammalian α crystallin is a small heat shock protein with chaperone-like ability, that is, it prevents the aggregation and precipitation of heat-damaged proteins. Using in vitro chaperone assays the team found that fish α crystallins protect same-species γ crystallins from heat damage, just like mammalianα crystallins do. But cow α crystallins did not protect toothfishγ crystallins from soaring temperatures. The team suggests that structural changes in the toothfish proteins prevent cow α and toothfishγ crystallins from interacting successfully. These structural changes likely reflect the evolutionary changes that enabled the Antarctic toothfish eye lens to adapt to extreme cold. So the Antarctic toothfish has its uniqueγ crystallins to thank for perfect vision in its frigid home.