Comparison of Zebrafish and Human -crystallin Chaperone Activity

Abstract

Abstract: : Purpose: The zebrafish (Danio rerio) has the potential to be a powerful model organism for the study of α-crystallin. We previously reported the amino acid sequences and tissue specific expression for zebrafish αA- and αB-crystallin. Here we compare the chaperone activity of these proteins to human αB-crystallin. Methods: Recombinant zebrafish αA- and αB-crystallin were produced in Escherichia coli. CD spectroscopy was used to compare the structures of the recombinant zebrafish proteins to their human orthologues. The chaperone activity of each crystallin was assayed by measuring its ability to prevent the DTT induced aggregation of lactalbumin at temperatures from 25 to 40°C. Results: CD spectroscopy indicated that zebrafish αA-crystallin was similar in structure to its human orthologue. The zebrafish αB-crystallin spectrum showed some differences from its human orthologue between 270 and 290nm. Similar peaks appear in the zebrafish protein, but with reduced ellepticity. Chaperone assays demonstrated that zebrafish αB-crystallin has a decreased ability to prevent aggregation of lactalbumin compared to human αB-crystallin at all temperatures tested. The human orthologue showed at least fivefold greater protection. Zebrafish αA-crystallin, however, showed similar protection to human αB-crystallin at all temperatures. All three crystallins showed similar decreases in protection with decreasing temperature. Conclusions: Chaperone activity of the two zebrafish α-crystallins differed greatly. The low chaperone activity of zebrafish αB-crystallin and the previously reported lack of detectable expression in zebrafish heart and brain suggest that this protein plays a different role in the zebrafish compared to humans. While zebrafish αA-crystallin showed similar protection to human αB-crystallin, the decrease in chaperone activity with temperature would mean that it is much less effective at the physiological temperature of the zebrafish (28°C) than αB-crystallin in the human lens. The relatively low protection provided by zebrafish αB-crystallin may be due to the lack of four C-terminal amino acids found in all other examined vertebrates. The effect of this C-terminal truncation on zebrafish αB-crystallin chaperone activity will be examined by replacing the final four amino acids found in the human orthologue onto the zebrafish protein. These differences and similarities between zebrafish and human orthologues should be considered when using the zebrafish as a model organism in future α-crystallin studies.

Keywords: chaperones • protein structure/function