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Oxidation‐Induced Structural Alterations and Its Effect on Chaperone Function of Rat Lens α‐Crystallin
Author(s) -
Ho Yuh,
Lai ChienLin,
Huang FuYung
Publication year - 1998
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.199800067
Subject(s) - chemistry , crystallin , tryptophan , circular dichroism , fluorescence , protein secondary structure , chaperone (clinical) , biophysics , protein tertiary structure , amino acid , crystallography , biochemistry , medicine , physics , pathology , quantum mechanics , biology
An ascorbate‐FeCl 3 ‐EDTA‐H 2 O 2 system was used to oxidize rat lens α‐crystallins. Under this oxidative insult, the chaperone activity of α‐crystallin toward γ‐crystallin was shown to decrease significantly, which is quite different from the result reported by Wang and Spector. ( Invest. Ophthalmol. Vis. Sci . 1995 , 36 , 311‐321.) Fluorescence spectroscopy and circular dichroism were employed to characterize the structural changes of oxidized α‐crystallin. It was found that fluorescence intensity of l‐anilinonaphthalene‐8‐sul‐phonate (ANS) bound to oxidized α‐crystallin increased comparing to that bound to normal α‐crystallin, suggesting oxidation causes the exposure of more hydrophobic regions. Further, α‐crystallin's fluorescence intensity in response to tryptophan residues showed a pseudo first order decline. Amino acid analysis of normal versus oxidized α‐crystallin confirmed actual decline in tryptophan levels, showing about 80% of tryptophan being modified after 10‐hour oxidation. Circular dichroism showed both changes in the secondary and tertiary structures of oxidized α‐crystallin, characterized by a large loss of aromatic‐type amino acid interactions and a large loss of β‐sheet structure. In conclusion, modified tryptophan, secondary and tertiary structural changes of α‐crystallin correlate best with the reduction of chaperone function, the curves all showing a linear slope for 10 hours, then plateauing. These results indicate that the decrease of α‐crystallin chaperone activity is attributed to the structural changes.