Temperature-dependent coaggregation of eye lens αB- and β-crystallins

Crystallin is essential not only for the maintenance of eye lens transparency, but also in the biology of other tissues. Eye lens α-crystallin exists as a heteropolymer composed of two homologous subunits, αA and αB. Despite the critical role of α-crystallin in many tissues, little is known regarding structural and functional significance of the two subunits. Herein, we describe a unique feature of αB-crystallin. At high temperatures (>70°C) not only αB-crystallin aggregates but also enhances the aggregation of other lens proteins. Intriguingly, αB-crystallin-mediated coaggregation at and above 70°C involves β- but not γ-crystallin. Further, αA-crystallin, but not a mutant (F71L) αA-crystallin, prevented aggregation of αB-crystallin and also reduced coaggregation of αB- and β-crystallin. These studies explain the rationale for the existence of α-crystallin heteropolymer with αA subunit as a major partner that is vital for lens transparency and provide insights into αB-crystallin-induced coaggregation which may have a bearing in some pathological conditions where αB-crystallin is overexpressed.