SAXS and SANS Observations of Abnormal Aggregation of Human α ‐Crystallin

Aggregation states of human α ‐crystallins are observed complementarily using small‐angle X‐ray and small‐angle neutron scatterings (SAXS and SANS). Infant α ‐crystallin is almost a monodispersed system of the aggregates with gyration radius of ca. 60 Å, which is a normal aggregate. On the other hand, the aged and cataract α ‐crystallins have not only the normal but also the larger aggregates. In the aged α ‐crystallin, the normal aggregate is a major component, but in the cataract α ‐crystallin the larger ones are dominant. Both α A‐ and α B‐crystallins, which are subunits of α ‐crystallin, also form an aggregate with the size close to the normal aggregate. Under UV irradiation, only aggregates of α B‐crystallin undergo further aggregation. Therefore, considering increase of ratio of α B‐crystallin in the aggregate of α ‐crystallin as aging, the abnormal aggregation (formation of the huge aggregates) mainly results in the further aggregation of α B‐crystallin caused by external stresses.