α-Crystallin-like Molecular Chaperone against the Thermal Denaturation of Lens Aldose Reductase: The Effect of Divalent Metal Ions

Marini, I; Bucchioni, L; Voltarelli, M; Corso, Antonella Del; Mura, Umberto

doi:10.1006/bbrc.1995.1985

Cited by 26 publications

(19 citation statements)

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“…Calcium and magnesium ions were able to antagonize the protective action of ␣-crystallin against the thermally induced aggregation of SDH as shown previously for aldose reductase and ␥-crystallin (28,29). In fact, both metal ions added at a millimolar level at 55°C to a transparent mixture of SDH and ␣-crystallin led to protein precipitation (Fig.…”

Section: Discussionsupporting

confidence: 73%

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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Section: Discussionsupporting

confidence: 73%

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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“…However, c~-crystallin has itself a strong tendency towards aggregation on thermal denaturation [12]. This phenomenon, which is also well known from previous calorimetric studies, affects the postdenaturational baseline and renders any quantitative determination of thermodynamic quantities difficult.…”

Section: Resultsmentioning

confidence: 95%

The conformational stability of α‐crystallin is rather low: Calorimetric results

Gesierich

Pfeil

1996

FEBS Letters

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The eye lens protein and chaperonin, ct-crystallin, was studied by differential scanning microcalorimetry, spectroscopy and size exclusion chromatography. The thermal transition of c¢-crystallin proceeds at Ttrs --59.8 _+ 0.6°C with an enthalpy change of AH=336+9 kJ per mol subunit. Disagreement between previous AH values could be attributed to a side reaction that leads, depending on the scan rate, to the formation of a nonproductive folding form. The conformational stability of acrystallin is rather low (AG= 24+5 kJ/mol of subunit). The minimal cooperative unit of ot-crystallin is the monomeric subunit.

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“…The aggregation of these natural substrates is also prevented by -crystallin during various conditions such as thermal stress and UV-light-induced stress. 7,22,23 This promiscuity raises questions as to how and what key features in a protein molecule it searches for recognition. However, it is generally believed that chaperones get activated when new hydrophobic sites of the substrates tend to get exposed and that hydrophobic interaction plays a major role in chaperone function; but it is not known whether such interaction is fully nonspecific.…”

Section: Introductionmentioning

confidence: 99%

Differential recognition of natural and nonnatural substrate by molecular chaperone α‐crystallin—A subunit exchange study

Biswas

Das

2006

Biopolymers

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Abstractα‐Crystallin is a molecular chaperone that recognizes proteins substrates in stress. It binds to the unstable conformer of a large variety of related or unrelated substrates and thus prevents them aggregating and holds them in a folding competent state. In this article, we have tried to critically analyze, from experimental point of view, whether α‐crystallin has any preference for its natural substrates compared to the nonnatural one. Our results clearly show that α‐crystallin is exceptionally active and sensitive in preventing aggregation of its natural substrates and can fully prevent such an aggregation in a substoichiometric ratio, but nonnatural substrates require a considerably higher amount of α‐crystallin. Using suitable fluorescent‐labeled α‐crystallins and performing fluorescence resonance energy transfer experiments, we were able to determine the subunit exchange kinetics between the α‐crystallin oligomers. It was found that while α‐crystallin was bound to its natural substrate, the rate of subunit exchange was slightly decreased. But, when a nonnatural substrate carbonic anhydrase remained bound to the chaperone, further loss in subunit exchange rate was observed. Nonnatural substrate was found to create higher activation energy barrier for the subunit exchange reaction compared to the native substrates. Similarities in major β‐sheet structure of both α‐crystallin and its natural substrates may be the reason for the preference in molecular recognition in comparison with the nonnatural substrate. © 2006 Wiley Periodicals, Inc. Biopolymers 85:189–197, 2007.This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com

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α-Crystallin-like Molecular Chaperone against the Thermal Denaturation of Lens Aldose Reductase: The Effect of Divalent Metal Ions

Cited by 26 publications

References 0 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 conformational stability of α‐crystallin is rather low: Calorimetric results

Differential recognition of natural and nonnatural substrate by molecular chaperone α‐crystallin—A subunit exchange study

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