title: Characterization of gamma S-crystallin isoforms from lip shark (Chiloscyllium colax): evolutionary comparison between gamma S and beta/gamma crystallins.
abstract: gamma S-Crystallin from shark eye lenses, formerly termed beta s crystallin in mammalian lenses, is structurally characterized in this study by cDNA cloning and sequencing. To facilitate sequence characterization of gamma S-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 gamma S-crystallins. Sequencing several positive clones revealed that a multiplicity of isoforms exists in the gamma S-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 gamma S1 and gamma S2 cDNAs with those published sequences of beta-, gamma-, and gamma S crystallins from bovine, human, bullfrog and carp lenses indicated that there is about 35-64% sequence homology between shark gamma S crystallins and structurally related crystallins from different evolutionary classes, with a higher sequence similarity between shark gamma S and mammalian gamma-crystallins than that of shark gamma S and carp gamma S or bovine gamma S crystallins. A phylogenetic tree constructed on the basis of the sequence divergence among various beta-, gamma-, and gamma S crystallins corroborates the closer relatedness of shark gamma S to authentic gamma-crystallin than to mammalian and teleostean gamma S crystallins. It further strengthens the supposition that ancestral precursors of gamma S-crystallins were present in the shark lens long before the appearance of present-day teleostean and mammalian gamma S-crystallins.
authors.affiliation: Laboratory of Crystallin Research, National Taiwan University, Taipei.
authors.forename: F M
authors.initials: FM
authors.lastname: Pan
authors.forename: M H
authors.initials: MH
authors.lastname: Chuang
authors.forename: S H
authors.initials: SH
authors.lastname: Chiou
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002347:Carps; D002417:Cattle; D003459:Crystallins / Q000737:chemistry* / Q000235:genetics*; D018076:DNA, Complementary / Q000737:chemistry; D019143:Evolution, Molecular; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry; D008969:Molecular Sequence Data; D010802:Phylogeny; D011892:Rana catesbeiana; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012754:Sharks / Q000235:genetics*; D013237:Stereoisomerism
chemical_list: D003459:Crystallins; D018076:DNA, Complementary