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. 2022 Aug 19;23(16):9347.
doi: 10.3390/ijms23169347.

Conformational Changes of α-Crystallin Proteins Induced by Heat Stress

Yu-Yung Chang  1 , Meng-Hsuan Hsieh  1 , Yen-Chieh Huang  1 , Chun-Jung Chen  1   2   3   4 , Ming-Tao Lee  1   5
Affiliations

Conformational Changes of α-Crystallin Proteins Induced by Heat Stress

Yu-Yung Chang et al. Int J Mol Sci. .

Abstract

α-crystallin is a major structural protein in the eye lenses of vertebrates that is composed of two relative subunits, αA and αB crystallin, which function in maintaining lens transparency. As a member of the small heat-shock protein family (sHsp), α-crystallin exhibits chaperone-like activity to prevent the misfolding or aggregation of critical proteins in the lens, which is associated with cataract disease. In this study, high-purity αA and αB crystallin proteins were expressed from E. coli and purified by affinity and size-exclusion chromatography. The size-exclusion chromatography experiment showed that both αA and αB crystallins exhibited oligomeric complexes in solution. Here, we present the structural characteristics of α-crystallin proteins from low to high temperature by combining circular dichroism (CD) and small-angle X-ray scattering (SAXS). Not only the CD data, but also SAXS data show that α-crystallin proteins exhibit transition behavior on conformation with temperature increasing. Although their protein sequences are highly conserved, the analysis of their thermal stability showed different properties in αA and αB crystallin. In this study, taken together, the data discussed were provided to demonstrate more insights into the chaperone-like activity of α-crystallin proteins.

Keywords: chaperone activity; circular dichroism; small-angle X-ray scattering; α-crystallin.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
CD spectra of (A) αA and (B) αB crystallin from 2 °C to 95 °C in 20 mM phosphate buffer (pH 7.4, 2 mM NaCl).
Figure 2
Figure 2
Representative (A) thermostability and (B) temperature reverse for αA and αB crystallin measured by circular dichroism. Circular dichroism signals at 212 nm were monitored at the rate of 1 °C/min from 25 to 95 °C and −5 °C/min from 95 to 25 °C, respectively.
Figure 3
Figure 3
Chaperone-like activity of α-crystallins for the chemical- and heat-induced aggregation of target proteins. Assays were performed at 37 °C for insulin and lysozyme and 55 °C for alcohol dehydrogenase, ADH. Curves indicate the aggregation of insulin (A), lysozyme (B) or ADH (C) alone or with αA or αB crystallin. Chaperone activity was represented as aggregation fraction (D–F). Assays were performed in triplicate and the bars represent the mean ± SD.
Figure 4
Figure 4
(A) SAXS profile of α-crystallins at various temperatures. Upon increasing temperature, the scattering pattern significantly changed in q range between 0.03 and 0.1 Å−1 (inset), indicating that morphologies changed with increasing temperature. (B) Evolution of the radius of gyration (Rg) of α-crystallins as a function of various temperatures. The effects of temperature rising on the structure of α-crystallins are reflected in the increase in Rg.
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