Characterization of gammaS-Crystallin Isoforms from Lip Shark (Chiloscyllium colax): Evolutionary Comparison between gammaS and beta/gamma Crystallins

Author： Pan F.M. Chuang M.H. Chiou S.H.

Publisher： Elsevier

ISSN： 0006-291X

Source： Biochemical and Biophysical Research Communications, Vol.240, Iss.1, 1997-11, pp. : 51-56

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Abstract

gammaS-Crystallin from shark eye lenses, formerly termed betas crystallin in mammalian lenses, is structurally characterized in this study by cDNA cloning and sequencing. To facilitate sequence characterization of gammaS-crystallin possessing intermediate structural properties between beta- and gamma-crystallins, cDNA mixture was constructed from the poly(A)+mRNA isolated from shark eye lenses, and amplification by polymerase chain reaction (PCR) was carried out to obtain nucleotide segments encoding multiple shark gammaS-crystallins. Sequencing several positive clones revealed that a multiplicity of isoforms exists in the gammaS-crystallin class of this cartilaginous fish, similar to authentic gamma-crystallin family characterized from the same shark species. Comparison of protein sequences encoded by two representative shark gammaS1 and gammaS2 cDNAs with those published sequences of beta-, gamma-, and gammaS crystallins from bovine, human, bullfrog and carp lenses indicated that there is about 35-64% sequence homology between shark gammaS crystallins and structurally related crystallins from different evolutionary classes, with a higher sequence similarity between shark gammaS and mammalian gamma-crystallins than that of shark gammaS and carp gammaS or bovine gammaS crystallins. A phylogenetic tree constructed on the basis of the sequence divergence among various beta-, gamma-, and gammaS crystallins corroborates the closer relatedness of shark gammaS to authentic gamma-crystallin than to mammalian and teleostean gammaS crystallins. It further strengthens the supposition that ancestral precursors of gammaS-crystallins were present in the shark lens long before the appearance of present-day teleostean and mammalian gammaS-crystallins. Copyright 1997 Academic Press.