α-Crystallins, versatile stress-proteins

Boelens, Wilbert C.; Jong, Wilfried W. de

doi:10.1007/bf00986495

Cited by 24 publications

(21 citation statements)

References 89 publications

(89 reference statements)

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“…Believed to be strictly a lens-specific protein, ␣-crystallin has now been found in several cells and non-lenticular tissues (1,2). Both ␣A and ␣B chains have a conserved domain, called the "␣-crystallin domain," which is peculiar to the SHSP 1 family (3,4). Like SHSP, ␣-crystallin subunits can be induced by heat and other stress conditions (5) and appear to be involved in the pathogenesis of various degenerative diseases (6,7) and in apoptosis (8).…”

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Complete Protection by α-Crystallin of Lens Sorbitol Dehydrogenase Undergoing Thermal Stress

Marini

Moschini

Corso

et al. 2000

Journal of Biological Chemistry

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Sorbitol dehydrogenase (L-iditol:NAD؉ 2-oxidoreductase, E.C. 1.1.1.14) (SDH) was significantly protected from thermally induced inactivation and aggregation by bovine lens ␣-crystallin. An ␣-crystallin/SDH ratio as low as 1:2 in weight was sufficient to preserve the transparency of the enzyme solution kept for at least 2 h at 55°C. Moreover, an ␣-crystallin/SDH ratio of 5:1 (w/w) was sufficient to preserve the enzyme activity fully at 55°C for at least 40 min. The protection by ␣-crystallin of SDH activity was essentially unaffected by high ionic strength (i.e. 0.5 M NaCl). On the other hand, the transparency of the protein solution was lost at a high salt concentration because of the precipitation of the ␣-crystallin/SDH adduct. Magnesium and calcium ions present at millimolar concentrations antagonized the protective action exerted by ␣-crystallin against the thermally induced inactivation and aggregation of SDH. The lack of protection of ␣-crystallin against the inactivation of SDH induced at 55°C by thiol blocking agents or EDTA together with the additive effect of NADH in stabilizing the enzyme in the presence of ␣-crystallin suggest that functional groups involved in catalysis are freely accessible in SDH while interacting with ␣-crystallin. Two different adducts between ␣-crystallin and SDH were isolated by gel filtration chromatography. One adduct was characterized by a high M r of approximately 800,000 and carried exclusively inactive SDH. A second adduct, carrying active SDH, had a size consistent with an interaction of the enzyme with monomers or low M r aggregates of ␣-crystallin. Even though it had a reduced efficiency with respect to ␣-crystallin, bovine serum albumin was shown to mimic the chaperone-like activity of ␣-crystallin in protecting SDH from thermal denaturation. These findings suggest that the multimeric structural organization of ␣-crystallin may not be a necessary requirement for the stabilization of the enzyme activity.

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Complete Protection by α-Crystallin of Lens Sorbitol Dehydrogenase Undergoing Thermal Stress

Marini

Moschini

Corso

et al. 2000

Journal of Biological Chemistry

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“…A-Crystallin is a major eye lens protein, composed of two types of subunits, AA-crystallin and AB-crystallin (for reviews see [6,7]). The latter also occurs at high levels in other tissues, notably in heart and striated muscle [8].…”

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The mammalian small heat‐shock protein Hsp20 forms dimers and is a poor chaperone

Klundert

Smulders

Gijsen

et al. 1998

European Journal of Biochemistry

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Hsp20 is one of the newly described members of the mammalian small heat-shock protein (sHsp) family. It occurs most abundantly in skeletal muscle and heart. We isolated clones for Hsp20 from a rat heart cDNA library, and expressed the protein in Escherichia coli to characterize this little known sHsp. Recombinant Hsp20 displayed similar far-ultraviolet circular dichroism spectra as the most closely related sHsp, AB-crystallin, but was less heat stable, denaturing upon heating to 50°C. While other mammalian recombinant sHsps form large multimeric complexes, Hsp20 occurs in two complex sizes, 43-kDa dimers and 470-kDa multimers. The ratio between the two forms depends on protein concentration. Moreover, Hsp20 has a much lower chaperone-like activity than AB-crystallin, as indicated by its relatively poor capacity to diminish the reduction-induced aggregation of insulin B chains. Hsp20 is considerably shorter at the C-terminus and less polar than other sHsps, but 1 H-NMR spectroscopy reveals that the last 10 residues are flexible, as in the other sHsps. Our findings suggest that Hsp20 is a special member of the sHsp family in being less heat stable and tending to form dimers. These properties, together with the shorter and less polar C-terminal extension, may contribute to the less effective chaperone-like activity.Keywords : small heat-shock protein; dimer ; oligomer; chaperone-like activity ; protein structure.In mammals, six members of the ubiquitous superfamily of small heat-shock proteins (sHsp) are known to occur [1]. These are AA-and AB-crystallin, Hsp25 (depending on species, also indicated as Hsp27 or Hsp28), the more recently discovered p20 [2], (now dubbed Hsp20 [3]), and the latest additions, HSPB2[4] and HspB3 [5]. A-Crystallin is a major eye lens protein, composed of two types of subunits, AA-crystallin and AB-crystallin (for reviews see [6,7]). The latter also occurs at high levels in other tissues, notably in heart and striated muscle [8]. AB-crystallin is stress-inducible [9] and its level is increased in various neurodegenerative disorders and tumors [10Ϫ13]. Hsp25 occurs at low levels in various tissues and is also inducible upon stress (for review see [14]). Both A-crystallins and Hsp25 display ATP-independent chaperone-like properties and confer thermotolerance upon expression in cultured cells. Mammalian A-crystallins and Hsp25 have been studied extensively. In contrast, Hsp20 has been the subject of only four reports [2,3,15,16], while HSPB2 and HspB3 are, as yet, the least known [4,5]. Hsp20 was originally isolated in mixed complexes with AB-crystallin and Hsp25 from rat and human skeletal muscle, and its amino acid sequence is most similar to AB-crystallin [1, 2]. Hsp20 was detected in all rat tissues examined, reaching the highest levels (up to 1.3 % of total protein) in striated muscle, heart and diaphragm, similar to AB-crystallin and Hsp25. Like Hsp25, it is also conspicuously present in smooth muscle of the bladder and rectum. Hsp20 exists in muscle extracts in a multimeric and a disso...

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“…It is an abundant structural protein in the vertebrate eye lens (1). Outside the lens it is especially expressed in tissues with high oxidative activity such as heart, striated muscle, and kidney, but also in degenerative disorders of the nervous system (2-4).…”

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“…Outside the lens it is especially expressed in tissues with high oxidative activity such as heart, striated muscle, and kidney, but also in degenerative disorders of the nervous system (2-4). ␣B-Crystallin belongs to the family of small heat shock proteins (sHsps) 1 (5,6). The sHsps vary in molecular mass between 12 and 43 kDa and are characterized by the presence of an 80 -100-amino acid long conserved C-terminal region.…”

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Negative Charges in the C-terminal Domain Stabilize the αB-Crystallin Complex

Boelens

Croes

Ruwe

et al. 1998

Journal of Biological Chemistry

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␣B-Crystallin is one of the six known mammalian small heat-shock proteins (sHsps). These are characterized by the presence of a conserved sequence of 80 -100 residues, which constitutes the putative C-terminal domain. Like other sHsps, ␣B-crystallin forms multimeric globular complexes, often in combination with related sHsps. Here we show that in a yeast two-hybrid system, ␣B-crystallin can specifically interact with itself as well as with ␣A-crystallin and Hsp27. Analyses of the separate domains show that the conserved C-terminal domain (C␣B) is essential for this interaction between subunits. To try and detect residues that are important in subunit interaction, the C␣B domain was used in a twohybrid screen as bait to select randomly mutated C␣B mutants. In this way we obtained nine mutants that were still able to interact with wild-type C␣B despite the presence of up to 15 replacements. Similarly, we obtained 16 mutants that were unable to bind, because of the presence of just three to nine replacements. In binding C␣B mutants, lysine residues were most often replaced by glutamic acid residues, and in non-binding C␣B mutants, acidic residues were often found to be replaced by non-charged residues. This indicates that negative charges are important for subunit interaction and we propose a model to explain this role of acidic residues. Furthermore, we observed that two homologs of ␣B-crystallin, ␣A-crystallin and Hsp27, generally interact similarly with the binding and non-binding C␣B mutants as does ␣B-crystallin. This suggests that interactions involved in the complex formation of these three sHsps are largely comparable.␣B-Crystallin is a protein with dual function. It is an abundant structural protein in the vertebrate eye lens (1). Outside the lens it is especially expressed in tissues with high oxidative activity such as heart, striated muscle, and kidney, but also in degenerative disorders of the nervous system (2-4). ␣B-Crystallin belongs to the family of small heat shock proteins (sHsps) 1 (5, 6). The sHsps vary in molecular mass between 12 and 43 kDa and are characterized by the presence of an 80 -100-amino acid long conserved C-terminal region. Most members of this family form large globular particles, up to 700 kDa in size, which can consist of a variable number of subunits.They are capable of preventing the aggregation of unfolding proteins (7-9). This chaperone-like activity may contribute to the most important in situ property of the sHsps, namely their ability to increase the stress tolerance of cells (10). In many cell types ␣B-crystallin is constitutively expressed, while in others the expression can be induced by different kinds of stress (11,12). In normal cells, ␣B-crystallin is mainly present as a soluble cytoplasmic protein. It can form mixed complexes with ␣A-crystallin, as well as with Hsp27 and Hsp20 (9, 13-16). Under certain stress conditions, ␣B-crystallin interacts with intermediate filaments, and in this way it is probably able to modulate the intermediate network (17)(18)(19).The t...

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α-Crystallins, versatile stress-proteins

Cited by 24 publications

References 89 publications

Complete Protection by α-Crystallin of Lens Sorbitol Dehydrogenase Undergoing Thermal Stress

Complete Protection by α-Crystallin of Lens Sorbitol Dehydrogenase Undergoing Thermal Stress

The mammalian small heat‐shock protein Hsp20 forms dimers and is a poor chaperone

Negative Charges in the C-terminal Domain Stabilize the αB-Crystallin Complex

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