Heat treatment of soluble proteins isolated from human cataract lens leads to the formation of non-fibrillar amyloid-like protein aggregates

Abstract

The loss of crystallins solubility with aging and the formation of amyloid-like aggregates is considered the hallmark characteristic of cataract pathology. The present study was carried out to assess the effect of temperature on the soluble lens protein and the formation of protein aggregates with typical amyloid characteristics. The soluble fraction of lens proteins was subjected for heat treatment in the range of 40-60 °C, and the nature of protein aggregates was assessed by using Congo red (CR), thioflavin T (ThT), and 8-anilinonaphthalene-1-sulfonic acid (ANS) binding assays, circular dichroism (CD), Fourier-transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM). The heat-treated protein samples displayed a substantial bathochromic shift (≈15 nm) in the CR's absorption maximum (λ_max) and increased ThT and ANS binding. The heat treatment of lens soluble proteins results in the formation of nontoxic, β-sheet rich, non-fibrillar, protein aggregates similar to the structures evident in the insoluble fraction of proteins isolated from the cataractous lens. The data obtained from the present study suggest that the exposure of soluble lens proteins to elevated temperature leads to the formation of non-fibrillar aggregates, establishing the role of amyloid in the heat-induced augmentation of cataracts pathology.

Keywords: Amyloids; Cataract; Crystallins; Protein aggregation; Soluble lens protein.