Eye Lens Proteins and Cataracts.

At first sight, the lens of the eye would appear to be an ideal environment for amyloid fibril formation. The protein concentration is the highest of any tissue in the body, the proteins are very long-lived, present in slightly acidic conditions and subjected over time to extensive truncation and post-translational modification. In addition, it has been demonstrated that lens crystallins can readily be induced to form amyloid fibrils in vitro. The situation may be further exacerbated after the onset of age-related nuclear cataract, which is characterized by massive oxidation of cysteine and methionine residues, accompanied by protein unfolding. Despite this, there is as yet no evidence for amyloid fibril formation in either the aged or the cataract human lens. Paradoxically, the reason may have to do with the supramolecular ordered β-sheet array that crystallins adopt once they are packed into mature fiber cells. This extended matrix in normal lenses displays some of the classic features normally associated with amyloid, for example, staining with Congo red and thioflavine T. [ABSTRACT FROM AUTHOR]