KISS, A.J.; DEVRIES, A.L.; CHENG, C-H.C.; University of Illinois at UC: Cold stable eye lens crystallins from the Antarctic nototheniid toothfish: A new model system to understand human cataracts.

The Antarctic toothfish (Dissostichus mawsoni) that inhabits the perennially freezing (�2&degC) seawater surrounding the Antarctic continent in the Southern Ocean has a completely transparent eye lens, whereas endothermic mammalian lenses undergo a cold-induced cataract below 20&degC. We have compared the lens crystallin composition of the Antarctic toothfish and the sub-tropical bigeye tuna (18&degC) to the endothermic cow (37&degC) model system using SEC & IEX chromatography, SDS & IEF PAGE, and chaperone assays. Each species contained all three ubiquitous vertebrate crystallins (α, β, γ) with both fish having lesser amounts of α and β, but twice as much γ crystallins than cow. Alpha crystallin from all three species was demonstrated to be a sHSP with chaperone-like ability to protect labile protein in thermal and chemical denaturation assays. Remarkably, we found that cow α crystallin could not protect heat-labile toothfish γ crystallin. As mammalian γ crystallins have been implicated in cold-cataract formation, we hypothesize that necessary cold adaptive structural changes in toothfish γ crystallins may have precluded their interaction with warm-bodied cow α crystallin. Isolation and sequencing of toothfish crystallin cDNAs indicates that α and β crystallins are homologous to their mammalian counterparts both in number and in sequence. We also found 12 unique toothfish γ crystallin cDNAs (twice that found in mammals), some of which are homologues of the γ crystallins from warm bodied mammals. Purification of individual toothfish γ crystallin protein isoforms is allowing detailed biochemical analysis, which when combined with cDNA sequence data should be instructive in understanding the basis for both the cold stability in toothfish lens and cold cataract in mammals.