Structural and functional alteration of human αA-crystallin after exposure to full spectrum solar radiation and preventive role of lens antioxidants

• Published in: International journal of biological macromolecules 2018-10, Vol.118, p.1120-1130
• Main Authors: Anbaraki, Afrooz, Ghahramani, Maryam, Muranov, Konstantin O., Kurganov, Boris I., Yousefi, Reza
• Format: Article
• Language: English
• Subjects: Chaperone-like activity; Human αA-crystallin; Lens antioxidants; Photosensitizer; Riboflavin
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2018.06.136

The chronically exposure of eye lenses to ultra violet and visible light of the solar radiation is an important risk factor for development of the senile cataract diseases. Various photosensitizer molecules including riboflavin (RF) play a significant role in photo-oxidative damages of lens proteins underlying development of opacity in the lenticular tissues. In the current study, RF-mediated photo-oxidation of human αA-crystallin (αA-Cry) was assessed using SDS-PAGE analysis, dynamic light scattering and other spectroscopic assessments. The RF-photosensitized reactions led to non-disulfide covalent cross-linking, oligomerization and significant structural changes in αA-Cry. The photo-damaging of αA-Cry under solar radiation was also accompanied by the reduction in both Trp and Tyr fluorescence intensities which followed by the formation of new photosensitizer chromophores. The solvent exposed hydrophobic patches, secondary structures and chaperone-like activity of αA-Cry were significantly altered after exposure to the solar radiation in the presence of RF. Although glutathione and ascorbate were capable to partially protect the photo-induced structural damages of human αA-Cry, they also disrupted its chaperone function when co-exposed with this protein to the solar radiation. Also, the most promising data were obtained with cysteine which its availability in the lenticular tissues is a rate limiting factor for the biosynthesis of glutathione. Overall our results suggest that glutathione and ascorbate, as the major anti-oxidant compounds within lenticular tissues, demonstrate controversial effect on structure and chaperone-like activity of human αA-Cry. Elucidation of this effect may demand further experiments. Lens crystallins are main pathogenic targets of the cataractogenic effect of UVA and visible light through the involvement of endogenous photosensitizer (PS) riboflavin which upon receiving solar radiation generates reactive oxygen species (ROS). Photo-oxidative damages of lens crystallins can accumulate over the lifespan which ultimately result in the cataract development. Before the middle age, in the adult human lenses, UV filter compounds absorb the solar radiations while do not themselves have photosensitizing effects, but release the energy before it has a chance to do any damage. After the middle age UV filters convert into destructive chromophores that absorbing photon energy and produce ROS which subsequently cause important damages to the