Crystallin distribution patterns in concentric layers from toad eye lenses

Abstract

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.

The Molecular Refractive Function of Lens γ-Crystallins

“…In contrast, γ crystallins, which exhibit the highest dn/dc values, are most abundant in the center with highest lens refractive index and highest protein concentration (440 – 500 mg/ml and higher 56,59,60 ). In the innermost regions of bovine and toad lenses, it was even found to provide nearly all of the soluble protein 61,62 . Generally, γ crystallins are also particularly prevalent in hard, high refractive index-lenses which are more closely packed, and relatively dehydrated 63,64 .…”

Optical Properties of In Situ Eye Lenses Measured with X-Ray Talbot Interferometry: A Novel Measure of Growth Processes

“…Lenses with steeper refractive index gradients and higher central index magnitudes have a greater proportion of the protein γ-crystallin [32]. This protein class has also been found to have the highest refractive increment [4] compared to the other crystallin proteins.…”

Primary sequence contribution to the optical function of the eye lens

“…In the case of cells from the central regions of lenses, protein synthesis has taken place during gestation and maintenance of optical quality is required for decades. The highest content of γ-crystallins is found in the central regions of mammalian lenses where refractive index reaches maximum magnitude31617; in cephalopods the predominant proteins which contribute to the high refractive index are S-crystallins31415. Both protein classes have relatively high refractive increments.…”

“…Across the crystallin isoforms differences in dn/dc values have been found, with the smallest of the crystallin classes: the γ-crystallins, having the highest dn/dc1314. This is also the crystallin class that is found in the core of the lens31617 where refractive index is the highest31819.…”