Crystallin distribution patterns in concentric layers from toad eye lenses

Protein distribution patterns across eye lenses from the Asiatic toad Bufo gargarizans were investigated and individual crystallin classes characterised. Special fractionation that follows the growth mode of the lens was used to yield nine fractions corresponding to layers laid down at different chronological (developmental) stages. Proportions of soluble and insoluble crystallins within each fraction were measured by Bradford assay. Water-soluble proteins in all fractions were separated by size-exclusion HPLC and constituents of each class further characterised by electrophoresis, RP-HPLC and MS analysis. In outer lens layers, alpha-crystallin is the most abundant soluble protein but is not found in soluble proteins in the lens centre. Water-soluble beta-crystallins also decrease from their highest level in the outer lens to negligible mounts in the central lens. The proportion of soluble gamma-crystallin increases significantly towards the lens centre where this is the only soluble protein present. Insoluble protein levels increase significantly towards the lens centre. In B. gargarizans lenses, as with other anurans, the predominant water-soluble protein class is gamma-crystallin. No taxon-specific crystallins were found. The relationship between the protein distribution patterns and the functional properties of the lens this species is discussed.