Chaperone-like Activity and Temperature-induced Structural Changes of α-Crystallin

Raman, Bakthisaran; Rao, Ch. Mohan

doi:10.1074/jbc.272.38.23559

Cited by 142 publications

(148 citation statements)

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“…Hydrophobic sites in α-crystallin are thought to be responsible for its chaperone activity [45,[134][135][136][137] and hydrophobic peptides isolated from αA-crystallin (residues 70-88) [137] and αB-crystallin (residues 73-92 and 131-141) [24, 138] possess chaperone activity against amorphously aggregating target proteins. The chaperone activity of these peptides results from their ability to bind independently to target proteins [137].…”

Section: The Region(s) Of α-Crystallin Responsible For Target Proteinmentioning

confidence: 99%

Crystallin proteins and amyloid fibrils

Ecroyd

Carver

2008

Cell. Mol. Life Sci.

221

234

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Improper protein folding (misfolding) can lead to the formation of disordered (amorphous) or ordered (amyloid fibril) aggregates. The major lens protein, alpha-crystallin, is a member of the small heat-shock protein (sHsp) family of intracellular molecular chaperone proteins that prevent protein aggregation. Whilst the chaperone activity of sHsps against amorphously aggregating proteins has been well studied, its action against fibril-forming proteins has received less attention despite the presence of sHsps in deposits found in fibril-associated diseases (e.g. Alzheimer's and Parkinson's). In this review, the literature on the interaction of alpha B-crystallin and other sHsps with fibril-forming proteins is summarized. In particular, the ability of sHsps to prevent fibril formation, their mechanisms of action and the possible in vivo consequences of such associations are discussed. Finally, the fibril-forming propensity of the crystallin proteins and its implications for cataract formation are described along with the potential use of fibrillar crystallin proteins as bionanomaterials. Improper protein folding (misfolding) can lead to the formation of disordered (amorphous) or ordered (amyloid fibril) aggregates. The major lens protein, α-crystallin, is a member of the small heat-shock protein (sHsp) family of intracellular molecular chaperone proteins that prevent protein aggregation. Whilst the chaperone activity of sHsps against amorphously aggregating proteins has been well studied, its action against fibril-forming proteins has received less attention despite the presence of sHsps in deposits found in fibril-associated diseases (e.g. Alzheimer's and Parkinson's). In this review, the literature on the interaction of αB-crystallin and other sHsps with fibril-forming proteins is summarized. In particular, the ability of sHsps to prevent fibril formation, their mechanisms of action and the possible in vivo consequences of such associations are discussed. Finally, the fibril-forming propensity of the crystallin proteins and its implications for cataract formation are described along with the potential use of fibrillar crystallin proteins as bionanomaterials.

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Section: The Region(s) Of α-Crystallin Responsible For Target Proteinmentioning

confidence: 99%

Crystallin proteins and amyloid fibrils

Ecroyd

Carver

2008

Cell. Mol. Life Sci.

221

234

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“…By using various non-thermal modes of aggregation, it was shown that chaperone-like activity of ␣-crystallin is temperature-dependent. A structural perturbation above 30°C enhances this activity severalfold (6,7). In order to probe the molecular mechanism of the chaperone-like activity and its enhancement upon structural perturbation, we have been studying ␣-crystallin and its constituent subunits.…”

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confidence: 99%

Domain Swapping in Human αA and αB Crystallins Affects Oligomerization and Enhances Chaperone-like Activity

Kumar¹,

Rao

2000

Journal of Biological Chemistry

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␣A and ␣B crystallins, members of the small heat shock protein family, prevent aggregation of proteins by their chaperone-like activity. These two proteins, although very homologous, particularly in the C-terminal region, which contains the highly conserved "␣-crystallin domain," show differences in their protective ability toward aggregation-prone target proteins. In order to investigate the differences between ␣A and ␣B crystallins, we engineered two chimeric proteins, ␣ANBC and ␣BNAC, by swapping the N-terminal domains of ␣A and ␣B crystallins. The chimeras were cloned and expressed in Escherichia coli. The purified recombinant wild-type and chimeric proteins were characterized by fluorescence and circular dichroism spectroscopy and gel permeation chromatography to study the changes in secondary, tertiary, and quaternary structure. Circular dichroism studies show structural changes in the chimeric proteins. ␣BNAC binds more 8-anilinonaphthalene-1-sulfonic acid than the ␣ANBC and the wild-type proteins, indicating increased accessible hydrophobic regions. The oligomeric state of ␣ANBC is comparable to wild-type ␣B homoaggregate. However, there is a large increase in the oligomer size of the ␣BNAC chimera. Interestingly, swapping domains results in complete loss of chaperone-like activity of ␣ANBC, whereas ␣BNAC shows severalfold increase in its protective ability. Our findings show the importance of the N-and C-terminal domains of ␣A and ␣B crystallins in subunit oligomerization and chaperone-like activity. Domain swapping results in an engineered protein with significantly enhanced chaperone-like activity.␣-Crystallin, a major lens protein having homology with small heat shock proteins (1-3), prevents aggregation of other proteins like a molecular chaperone (4). We had earlier shown that ␣-crystallin can prevent photo-aggregation of ␥-crystallin, which may have relevance in cataractogenesis (5). By using various non-thermal modes of aggregation, it was shown that chaperone-like activity of ␣-crystallin is temperature-dependent. A structural perturbation above 30°C enhances this activity severalfold (6, 7). In order to probe the molecular mechanism of the chaperone-like activity and its enhancement upon structural perturbation, we have been studying ␣-crystallin and its constituent subunits. Our recent study on the ␣A and ␣B homoaggregates showed that, despite high sequence homology, these proteins differ in their stability, chaperone-like activity, and the temperature dependence of this activity (8). This study also indicated different roles for the two proteins in the ␣-crystallin heteroaggregate in the eye lens and as separate proteins in non-lenticular tissues. Several investigators have introduced mutations in ␣A and ␣B crystallins to gain an insight into the structure-function relation (9 -12). Derham and Harding in their recent review (13) list about 30 sitedirected mutations from different laboratories. These mutations either result in some decrease or no change in the protective ability. It is interes...

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“…A structural transition above 30°C enhances the protective ability perhaps by increasing or reorganizing hydrophobic surfaces. We have recently shown that tertiary structural changes precede quaternary structural changes (20,21). ␣-Crystallin is a heteroaggregate of two gene products, ␣A-and ␣B-crystallin.…”

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confidence: 99%

Differential Temperature-dependent Chaperone-like Activity of αA- and αB-crystallin Homoaggregates

Datta

Rao

1999

Journal of Biological Chemistry

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104

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␣-Crystallin, a heteromultimeric protein made up of ␣A-and ␣B-crystallins, functions as a molecular chaperone in preventing the aggregation of proteins. We have shown earlier that structural perturbation of ␣-crystallin can enhance its chaperone-like activity severalfold. The two subunits of ␣-crystallin have extensive sequence homology and individually display chaperonelike activity. We have investigated the chaperone-like activity of ␣A-and ␣B-crystallin homoaggregates against thermal and nonthermal modes of aggregation. We find that, against a nonthermal mode of aggregation, ␣B-crystallin shows significant protective ability even at subphysiological temperatures, at which ␣A-crystallin or heteromultimeric ␣-crystallin exhibit very little chaperone-like activity. Interestingly, differences in the protective ability of these homoaggregates against the thermal aggregation of ␤ L -crystallin is negligible. To investigate this differential behavior, we have monitored the temperature-dependent structural changes in both the proteins using fluorescence and circular dichroism spectroscopy. Intrinsic tryptophan fluorescence quenching by acrylamide shows that the tryptophans in ␣B-crystallin are more accessible than the lone tryptophan in ␣A-crystallin even at 25°C. Protein-bound 8-anilinonaphthalene-1-sulfonate fluorescence demonstrates the higher solvent accessibility of hydrophobic surfaces on ␣B-crystallin. Circular dichroism studies show some tertiary structural changes in ␣A-crystallin above 50°C. ␣B-crystallin, on the other hand, shows significant alteration of tertiary structure by 45°C. Our study demonstrates that despite a high degree of sequence homology and their generally accepted structural similarity, ␣B-crystallin is much more sensitive to temperaturedependent structural perturbation than ␣A-or ␣-crystallin and shows differences in its chaperone-like properties. These differences appear to be relevant to temperature-dependent enhancement of chaperone-like activity of ␣-crystallin and indicate different roles for the two proteins both in ␣-crystallin heteroaggregate and as separate proteins under stress conditions. ␣-Crystallin is a major protein of the mammalian lens and constitutes as much as 50% of its dry weight. Studies over the past few years have shown that ␣-crystallin is expressed in several nonlenticular tissues such as heart, brain, and kidney, and its expression is enhanced severalfold during stress and disease conditions (1-6). ␣-Crystallin is shown to have homology with small heat shock proteins (7-10). Horwitz (11) shows that ␣-crystallin can prevent the thermal aggregation of ␤-and ␥-crystallins and a few other proteins like a molecular chaperone. Demonstration of chaperone-like activity of ␣-crystallin has provided an excellent opportunity to investigate the mechanistic aspects of chaperone function in general and the role of ␣-crystallin under stress conditions in particular. It is possible that, in the lens, ␣-crystallin may chaperone the formation of the transparent and appropriately ...

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Chaperone-like Activity and Temperature-induced Structural Changes of α-Crystallin

Cited by 142 publications

References 45 publications

Crystallin proteins and amyloid fibrils

Crystallin proteins and amyloid fibrils

Domain Swapping in Human αA and αB Crystallins Affects Oligomerization and Enhances Chaperone-like Activity

Differential Temperature-dependent Chaperone-like Activity of αA- and αB-crystallin Homoaggregates

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