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Gene duplication and separation of functions in αB‐crystallin from zebrafish ( Danio rerio )
Author(s) -
Smith Amber A.,
Wyatt Keith,
Vacha Jennifer,
Vihtelic Thomas S.,
Samuel Zigler J.,
Wistow Graeme J.,
Posner Mason
Publication year - 2006
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2005.05080.x
Subject(s) - zebrafish , crystallin , biology , danio , chaperone (clinical) , microbiology and biotechnology , gene , gene expression , biochemistry , pathology , medicine
We previously reported that zebrafish αB‐crystallin is not constitutively expressed in nervous or muscular tissue and has reduced chaperone‐like activity compared with its human ortholog. Here we characterize the tissue expression pattern and chaperone‐like activity of a second zebrafish αB‐crystallin. Expressed sequence tag analysis of adult zebrafish lens revealed the presence of a novel α‐crystallin transcript designated cryab2 and the resulting protein αB2‐crystallin. The deduced protein sequence was 58.2% and 50.3% identical with human αB‐crystallin and zebrafish αB1‐crystallin, respectively. RT‐PCR showed that αB2‐crystallin is expressed predominantly in lens but, reminiscent of mammalian αB‐crystallin, also has lower constitutive expression in heart, brain, skeletal muscle and liver. The chaperone‐like activity of purified recombinant αB2 protein was assayed by measuring its ability to prevent the chemically induced aggregation of α‐lactalbumin and lysozyme. At 25 °C and 30 °C, zebrafish αB2 showed greater chaperone‐like activity than human αB‐crystallin, and at 35 °C and 40 °C, the human protein provided greater protection against aggregation. 2D gel electrophoresis indicated that αB2‐crystallin makes up ≈ 0.16% of total zebrafish lens protein. Zebrafish is the first species known to express two different αB‐crystallins. Differences in primary structure, expression and chaperone‐like activity suggest that the two zebrafish αB‐crystallins perform divergent physiological roles. After gene duplication, zebrafish αB2 maintained the widespread protective role also found in mammalian αB‐crystallin, while zebrafish αB1 adopted a more restricted, nonchaperone role in the lens. Gene duplication may have allowed these functions to separate, providing a unique model for studying structure–function relationships and the regulation of tissue‐specific expression patterns.