title: Characterization of gammaS-crystallin isoforms from a catfish: evolutionary comparison of various gamma-, gammaS-, and beta-crystallins.
abstract: gammaS-Crystallin from catfish eye lenses, formerly designated betas-crystallin in mammalian lenses, is structurally characterized in this study by cDNA cloning and sequencing. To facilitate sequence characterization of gammaS-crystallin with structural properties lying between beta- and gamma-crystallins, a cDNA mixture was constructed from the poly(A)+ mRNA isolated from catfish eye lenses, and amplification by polymerase chain reaction (PCR) was carried out to obtain nucleotide segments encoding multiple gammaS-crystallin isoforms. Sequencing several positive clones revealed that at least two distinct isoforms exist in the gammaS-crystallin class of this teleostean fish, similar to the authentic gamma-crystallin family characterized previously in species of the piscine class. Comparison of protein sequences encoded by two representative catfish gammaS1 and gammaS2 cDNAs with the published sequences of beta-, gamma-, and gammaS-crystallins from shark, carp, bullfrog, bovine, and human lenses indicates that there is about 20-50% sequence homology between catfish gammaS-crystallins and various members of the related beta/gamma-crystallin superfamily from different evolutionary classes, with a higher sequence similarity being found between catfish gammaS- and mammalian gamma-crystallins than between catfish gammaS- and bovine or carp gammaS-crystallins. Phylogenetic trees constructed on the basis of the nucleotide and protein sequence divergence among various beta-, gamma-, and gammaS-crystallins corroborate the closer relatedness of catfish gammaS- to authentic gamma-crystallin than to bovine and carp gammaS-crystallins. The results suggest that evolution of catfish gammaS-crystallins follows a different path from that of bovine and carp gammaS-crystallins and may represent a more ancient offshoot from the ancestral gamma/gammaS coding gene than carp and bovine gammaS-crystallins.
authors.affiliation: Institute of Biochemical Sciences, National Taiwan University, Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan. shchiou@bc.ntu.edu.TW
authors.forename: S H
authors.initials: SH
authors.lastname: Chiou
authors.forename: F M
authors.initials: FM
authors.lastname: Pan
authors.forename: H W
authors.initials: HW
authors.lastname: Peng
authors.forename: Y K
authors.initials: YK
authors.lastname: Chao
authors.forename: W C
authors.initials: WC
authors.lastname: Chang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002397:Catfishes / Q000235:genetics*; D002417:Cattle; D003001:Cloning, Molecular; D003459:Crystallins / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D019143:Evolution, Molecular; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D003459:Crystallins; D017931:DNA Primers; D018076:DNA, Complementary; D012333:RNA, Messenger