Gene duplication and separation of functions in alphaB-crystallin from zebrafish (Danio rerio).
We previously reported that zebrafish alphaB-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 alphaB-crystallin. Expressed sequence tag analysis of adult zebrafish lens revealed the presence of a novel alpha-crystallin transcript designated cryab2 and the resulting protein alphaB2-crystallin. The deduced protein sequence was 58.2% and 50.3% identical with human alphaB-crystallin and zebrafish alphaB1-crystallin, respectively. RT-PCR showed that alphaB2-crystallin is expressed predominantly in lens but, reminiscent of mammalian alphaB-crystallin, also has lower constitutive expression in heart, brain, skeletal muscle and liver. The chaperone-like activity of purified recombinant alphaB2 protein was assayed by measuring its ability to prevent the chemically induced aggregation of alpha-lactalbumin and lysozyme. At 25 degrees C and 30 degrees C, zebrafish alphaB2 showed greater chaperone-like activity than human alphaB-crystallin, and at 35 degrees C and 40 degrees C, the human protein provided greater protection against aggregation. 2D gel electrophoresis indicated that alphaB2-crystallin makes up approximately 0.16% of total zebrafish lens protein. Zebrafish is the first species known to express two different alphaB-crystallins. Differences in primary structure, expression and chaperone-like activity suggest that the two zebrafish alphaB-crystallins perform divergent physiological roles. After gene duplication, zebrafish alphaB2 maintained the widespread protective role also found in mammalian alphaB-crystallin, while zebrafish alphaB1 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.
Smith
Amber A
AA
Department of Biology, Ashland University, OH 44805, USA.
Wyatt
Keith
K
Vacha
Jennifer
J
Vihtelic
Thomas S
TS
Zigler
J S
JS
Wistow
Graeme J
GJ
Posner
Mason
M
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D020440:Gene Duplication; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D013696:Temperature; D013997:Time Factors; D015027:Zebrafish / Q000235:genetics*; D038203:alpha-Crystallin B Chain / Q000235:genetics* / Q000502:physiology*
D038203:alpha-Crystallin B Chain