Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0086543 (cataract)
 29,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The conformational stabilities of bovine lens gamma-crystallin fractions II, IIIA, IIIB, and IVA and those modified with glutathione were compared by studying the thermal and guanidine hydrochloride (Gdn-HCl) denaturation behavior. The conformational state was monitored by both far-UV CD and fluorescence measurements. All the gamma-crystallins studied showed a sigmoidal order-disorder transition with varied melting temperatures. The thermal denaturation of these proteins is reversible up to a temperature 3 or 4 degrees C above T 1/2; above this temperature, irreversible aggregation occurs. The validity of a two-state approximation of both thermal and Gdn-HCl denaturation was tested for all four crystallins, and the presence of one or more intermediates was evident in the unfolding of IVA. delta GDH2O values of these crystallins range from 4 to 9 kcal/mol. Upon glutathione treatment IVA showed the maximum decrease in T 1/2 by approximately 9 degrees C and in delta GDH2O value by 29%; the smallest decrease in T 1/2 was for IIIA by 2 degrees C and in delta GDH2O by 15%. We have demonstrated that the glutathione reaction can dramatically reduce the conformational stability of gamma-crystallins and, thus, that the thermodynamic quantities of the unreacted crystallins can be used to evaluate the stability of these proteins when modified during cataract formation.
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PMID:Thermodynamics of thermal and athermal denaturation of gamma-crystallins: changes in conformational stability upon glutathione reaction. 230 85

Lens proteins labeled with the -SH-specific reagents N-(1-pyrene)-maleimide (PM) and N-(1-pyrene)-iodo-acetamide (PIA) exhibited pyrene excimer fluorescence around 480 nm. Among the gamma-fractions, only gamma II showed excimer band at room temperature with both probes PM and PIA. As the temperature increased, PM-labeled gamma IIIA, gamma IIIB, and gamma IV also began to exhibit excimer around 55 degrees C, which did not disappear at a very high temperature (85 degrees C). With PIA, gamma IIIA and gamma IVA did not show excimer at any temperature. The beta-crystallins, on the other hand, revealed a very strong excimer/monomer intensity ratio at room temperature, which decreased with an increase in temperature. Life-time measurements indicated a difference in the micro-environments around the labeled -SH residues. The origin of the excimer band as well as temperature effects on this band have been explained on the basis of intra- and inter-molecular interaction among the Cys residues in the lens proteins. The temperature-dependent CD studies further indicated retention of thermodynamic stability of the crystallins after chemical modifications. Both PM and PIA could be used conveniently to probe -SH proximity, determine the ease and extent of disulfide formation, and monitor the dynamics of lens protein conformation, all of which are critically important with regard to cataract formation.
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PMID:Proximity of sulfhydryl groups in lens proteins. Excimer fluorescence of pyrene-labeled crystallins. 238 49

High resolution calorimetry and spectral measurements have been employed to examine folding/unfolding behaviour of gamma-crystallins which are known to contain two homologous domains. Results have been analyzed in terms of selective unfolding of domains, interdomain interactions, conformational stability and the existence of intermediates in the order-disorder transition equilibrium. Both spectral and thermotropic data indicate that, in terms of structural hierarchy, these proteins can be divided into two distinct groups, gamma II and gamma IIIB belonging to one and gamma IIIA and gamma IVA to the other. The unfolding/folding characteristics of these two groups are distinctly different. Equilibrium unfolding of gamma II and gamma IIIB is biphasic indicating the existence of an intermediate in which one domain unfolds and the other remains in the native form. The absence of a cooperative transition in gamma IIIA and gamma IVA in acidic urea has also been attributed to a structured intermediate, most likely a molten globule, which may not be thermodynamically as distinct as of the former group. The difference in the equilibrium folding/unfolding transition of these two groups has been explained by subtle differences in the packing arrangement of their two domains and interactions between them. Since the intermediates, under certain circumstances, are known to aggregate, they are likely to play a critical role in the etiology of human cataract formation.
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PMID:Differential domain folding/unfolding of gamma-crystallins: existence of two distinct groups. 800 19