Physiological role of the association complexes of alpha-crystallin and its substrates on the chaperone activity.
Previous reports on the chaperone activity of alpha-crystallin to prevent protein denaturation and thermal aggregation have suggested that partially denatured proteins can bind alpha-crystallin in its central region. Likewise, beta- and gamma-crystallin can also be localized to the central cavity of alpha-crystallin particle in vivo, which provides indirect evidence that alpha-crystallin can function as a chaperone in the intact lens. In this study, we have further demonstrated that the binding of the substrate proteins to alpha-crystallin by short-term preincubation may mimic the in vivo conditions of crystallin association. Preheating of alpha-crystallin with its substrate proteins at 60 degrees C for 20 min resulted in the formation of stable complexes between alpha-crystallin and its substrates (8.0% of insulin or 5.3% of gamma-crystallin was involved in complex formation). Under such conditions, the chaperone activity of alpha-crystallin to inhibit dithiothreitol-, ultraviolet-, or oxidation-induced protein aggregation can be greatly enhanced. Since UV-irradiation and oxidative stress are common insults to eye lenses under normal physiological conditions, the presence of alpha/gamma and alpha/beta complex in vivo may play an important role to maintain the lens in a transparent state.
Lee
J S
JS
Department of Ophthalmology, Chang-Gung Memorial Hospital, Taipei, Taiwan.
Samejima
T
T
Liao
J H
JH
Wu
S H
SH
Chiou
S H
SH
D000818:Animals; D002417:Cattle; D003459:Crystallins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects; D066298:In Vitro Techniques; D007328:Insulin / Q000737:chemistry / Q000378:metabolism; D046911:Macromolecular Substances; D018832:Molecular Chaperones / Q000737:chemistry* / Q000502:physiology* / Q000528:radiation effects; D018384:Oxidative Stress; D011485:Protein Binding; D011489:Protein Denaturation; D014466:Ultraviolet Rays / Q000009:adverse effects
D003459:Crystallins; D007328:Insulin; D046911:Macromolecular Substances; D018832:Molecular Chaperones