Assignment of the αB-crystallin gene to human chromosome 11

“…These mutations either result in some decrease or no change in the protective ability. It is interesting to note that point mutations in both ␣A and ␣B crystallin, R116C and R120G, respectively, result in significant loss of activity and are associated with human diseases (14 -19).Human ␣A and ␣B crystallins are coded by three exons (20,21) and are thought to have arisen due to gene duplication. They share high sequence homology with the small heat shock proteins, which are found in all organisms, from prokaryotes to humans (22).…”

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confidence: 99%

“…Human ␣A and ␣B crystallins are coded by three exons (20,21) and are thought to have arisen due to gene duplication. They share high sequence homology with the small heat shock proteins, which are found in all organisms, from prokaryotes to humans (22).…”

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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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“…␣-Crystallin is one of the most abundant of the crystallins in mature lens fiber cells. It is a M r ϳ0.6 -1.0 ϫ 10 6 complex composed of two structurally related subunits, designated ␣A and ␣B, which are encoded by genes localized to chromosomes 21 and 11, respectively (4,5). While expression of the ␣A gene appears to be preferentially but not exclusively restricted to lens cells (6), the ␣B gene product has been described in a broad number of tissues and organs including the brain, skeletal muscle, heart, and kidney (7,8).…”

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Cloning, Expression, and Chaperone-like Activity of Human αA-Crystallin

Andley

Mathur

Griest

et al. 1996

Journal of Biological Chemistry

152

136

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One of the major protein components of the ocular lens, ␣-crystallin, is composed of ␣A and ␣B chain subunits that have structural homology to the family of mammalian small heat shock proteins. Like other small heat shock proteins, ␣-crystallin subunits associate to form large oligomeric aggregates that express chaperone-like activity, as defined by the ability to suppress nonspecific aggregation of proteins destabilized by treatment with a variety of denaturants including heat, UV irradiation, and chemical modification. It has been proposed that age-related loss of sequences at the C terminus of the ␣A chain subunit may be a factor in the pathogenesis of cataract due to diminished capacity of the truncated crystallin to protect against nonspecific aggregation of lens proteins. To evaluate the functional consequences of ␣-crystallin modification, two mutant forms of ␣A subunits were prepared by site-directed mutagenesis. Like wild type (WT), aggregates of ϳ540 kDa were formed from a tryptophan-free ␣A mutant (W9F). When added in stoichiometric amounts, both WT and W9F subunits completely suppressed the heat-induced aggregation of aldose reductase. In contrast, subunits encoded by a truncation mutant in which the Cterminal 17 residues were deleted (R157STOP), despite having spectroscopic properties similar to WT, formed much larger aggregates with a marked reduction in chaperone-like activity. Similar results were observed when the chaperone-like activity was assessed through inhibition of ␥-crystallin aggregation induced by singlet oxygen. These results demonstrate that the structurally conservative substitution of Phe for Trp-9 has a negligible effect on the functional interaction of ␣A subunits, and that deletion of C-terminal sequences from the ␣A subunit results in substantial loss of chaperone-like activity, despite overall preservation of secondary structure.The major components of the mammalian lens fiber cells are the ␣-, ␤-, and ␥-crystallins, which constitute an estimated 35% wet weight of the lens. The crystallins contribute to the transparency and refractive power of the lens by short range interactions among themselves and cytoskeletal elements in a highly concentrated matrix (1-3). ␣-Crystallin is one of the most abundant of the crystallins in mature lens fiber cells. It is a M r ϳ0.6 -1.0 ϫ 10 6 complex composed of two structurally related subunits, designated ␣A and ␣B, which are encoded by genes localized to chromosomes 21 and 11, respectively (4, 5).

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Assignment of the αB-crystallin gene to human chromosome 11

Cited by 36 publications

References 28 publications

Report of the committee on the genetic constitution of chromosome 11

Report of the committee on the genetic constitution of chromosome 11

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

Cloning, Expression, and Chaperone-like Activity of Human αA-Crystallin

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