The effects of ageing on the chaperone-like function of rabbit alpha-crystallin, comparing three methods of assay.

The lens has a high protein content necessary for focusing light on to the retina. Alpha-Crystallin accounts for approximately 40% of the protein and has been shown to act in a chaperone-like manner. Here we show the effects of ageing on the chaperone-like properties of alpha-crystallin from rabbit lens. Three assays were used to determine chaperone ability. Non-enzymatic glycosylation inactivation of malate dehydrogenase is protected by alpha-crystallin. Thermal aggregation of beta-low crystallin and malate dehydrogenase are both prevented by alpha-crystallin. Three ages of rabbit lens were used. Alpha-Crystallin from the soluble fraction of the cortex and nucleus were investigated as well as alpha-high and alpha-low fractions resolved by size-exclusion chromatography. All three methods complemented each other. There was no age-dependent loss in chaperone-like behaviour for both alpha fractions in the cortex. There was an early decrease with age of the nuclear alpha-low fraction. Nuclear alpha-high shows no age-related decrease but its chaperoning ability is greatly compromised. Post-translational modifications which occur during ageing may be responsible for the effect of alpha-crystallin chaperone-like ability in the lens nucleus.