Expression of duck lens delta-crystallin cDNAs in yeast and bacterial hosts. Delta 2-crystallin is an active argininosuccinate lyase.
The major soluble protein in the lenses of most birds and reptiles is delta-crystallin. In chickens and ducks the delta-crystallin gene has duplicated, and in the duck both genes contribute to the protein in the lens, while in the chicken lens there is a great preponderance of the delta 1 gene product. Purified delta-crystallin has previously been shown to possess the enzymatic activity of argininosuccinate lyase. In order to determine the enzymatic properties of the two duck delta-crystallins their corresponding cDNA molecules were placed in yeast and bacterial expression plasmids. In Saccharomyces cerevisiae, the activity of each crystallin was assessed by transformation of the expression plasmids into a strain deficient for argininosuccinate lyase activity. The ability of the resulting yeast to grow on arginine deficient medium was used as a measure of enzymatic activity. Yeast expressing the duck delta 2-crystallin protein grew rapidly, while those expressing delta 1-crystallin failed to grow. Enzyme activity measurements confirmed the presence of activity in the delta 2-crystallin-expressing yeast, and no detectable activity could be demonstrated in the delta 1-crystallin-expressing yeast. Northern blotting of RNA from the transformed yeast revealed equal levels of mRNA species from the two constructs. For further analysis, the delta 2-crystallin cDNA was placed in the bacterial expression plasmid, pET-3d. The delta 2-crystallin protein produced in Escherichia coli was purified to homogeneity and analyzed to determine the kinetic properties. A Km of 0.35 mM was determined for argininosuccinate and a Vm of 3.5 mumols/min/mg was determined. These data demonstrate that, following duplication of the primordial argininosuccinate lyase gene, one of the genes maintained its role as an enzyme (delta 2-crystallin) while also serving as a crystallin and the other has evolved to specialize as a structural protein in the lens (delta 1-crystallin), presumably losing most or all of its catalytic capacity.
Barbosa
P
P
Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030.
Wistow
G J
GJ
Cialkowski
M
M
Piatigorsky
J
J
O'Brien
W E
WE
D000818:Animals; D001123:Argininosuccinate Lyase / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D001483:Base Sequence; D015152:Blotting, Northern; D003001:Cloning, Molecular / Q000379:methods; D003459:Crystallins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D004247:DNA / Q000235:genetics* / Q000302:isolation & purification; D004372:Ducks; D004591:Electrophoresis, Polyacrylamide Gel; D005822:Genetic Vectors; D007700:Kinetics; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D010957:Plasmids; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics*
D003459:Crystallins; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D012313:RNA; D004247:DNA; D001123:Argininosuccinate Lyase