Short-range order of crystallin proteins accounts for eye lens transparency

Abstract

In its normal state, the eye lens is transparent despite the presence in the cell cytoplasm of high concentrations of proteins, the crystallins, which, a priori, could be expected to scatter an important part of the incident light. Early on, an explanation was sought in the spatial correlations between individual scatterers. Trokel first proposed that the "high concentration of proteins in the lens must be accompanied by a degree of local order approaching a paracrystalline state"; Benedek subsequently suggested that a dense, noncrystalline packing of the proteins would sufficiently reduce the scattered intensity. However, in spite of an improved understanding of the molecular structure of crystallins, their spatial order remained unknown. We present here a small-angle X-ray scattering study of the problem, performed with calf lens cytoplasm both in intact lenses and in cytoplasmic extracts where the crystallin concentration was varied from 3 to 510 mg ml-1. All our experimental data are consistent with short-range spatial order, as in dense liquids or glasses, and this provides a simple explanation for lens transparency. In addition, we detected no conformational change or reorganization of the crystallin proteins throughout the investigated concentration range.

Increased risk of cataract development in WNIN‐obese rats due to accumulation of intralenticular sorbitol

“…The transparency of eye lens is maintained by the exquisite packing of lens proteins and chaperone-like activity of acrystallin (26,27). It is believed that oxidative stress, osmotic stress, and nonenzymatic glycation of lens proteins result in altered structural and functional integrity either due to direct modification and/or due to reduced a-crystallin chaperone activity, resulting in lens protein aggregation and thus opacification (13)(14)(15)28).…”

The apparent molecular size of native α‐crystallin B in non‐lenticular tissues

“…Because bovine lens c+crystallin aggregates with apparent average molecular size of 0.8 x lo6 Da have been isolated under physiological conditions of temperature, pH and ionic strength, it is believed that they occur in the intact tissue in vivo [5], a concept which is supported by indirect evidence from spectroscopic studies of the lens tissue [25]. However, whether in the lens or in the other tissues, cu-crystallin aggregates are the result of particular interactions between the constitutive polypeptide molecules.…”

Genomic analysis of pediatric cataract in Saudi Arabia reveals novel candidate disease genes

“…2 Transparency of the lens is achieved by virtue of a number of unique properties that are both structural and functional. 3 For instance, lens fiber cells lack nuclei and organelles and are orchestrated in a highly structured pattern that minimizes intercellular spaces and endows a high refractive index. In addition, the lens is very rich in proteins, mostly crystallins, with unique optical properties.…”