Heterogeneity of gamma-crystallins from spiny dogfish (Squalus acanthias) eye lens

Characterization of gammaS-crystallin isoforms from a catfish: evolutionary comparison of various gamma-, gammaS-, and beta-crystallins

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.

Characterization of gamma S-crystallin isoforms from lip shark (Chiloscyllium colax): evolutionary comparison between gamma S and beta/gamma crystallins

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.

Sequence characterization of gamma-crystallins from lip shark (Chiloscyllium colax): existence of two cDNAs encoding gamma-crystallins of mammalian and teleostean classes

gamma-Crystallin is a common lens protein of most vertebrate eye lenses and the major protein component in lenses of fishes and in many mammalian species during embryonic and neonatal stages. To facilitate the structural characterization of gamma-crystallin possessing extensive charge heterogeneity, a 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 cDNAs encoding multiple shark gamma-crystallins. Sequencing analysis of multiple positive clones containing PCR-amplified inserts revealed the presence of a multiplicity of isoforms in the gamma-crystallin class of this cartilaginous fish. It was of interest to find that two shark cDNA sequences coexist, one encoding gamma-crystallin (gamma M1) of high methionine content (15.5%) and the other encoding one (gamma M2) of low methionine content (5.1%), each corresponding to the major teleostean and mammalian gamma-crystallins, respectively. Comparison of protein sequences encoded by these two shark cDNAs with published sequences of gamma-crystallins from mouse, bovine, human, frog, and carp lenses indicated that there is about 61-80% sequence homology between different species of the piscine class, whereas only 47-66% is found between mammals and shark. A phylogenetic tree constructed on the basis of sequence divergence among various gamma-crystallin cDNAs revealed the close relatedness between shark gamma M2-crystallin and mammalian gamma-crystallins and that between shark gamma M1 and teleostean gamma-crystallins. The results pointed to the fact that ancestral precursors of gamma-crystallins were present in the sharp lens long before the appearance of modern-day mammalian and teleostean gamma-crystallins.

Characterization of gamma-crystallins from eye lenses of shark: closer structural similarity to mammalian than other piscine gamma-crystallins?

Lens crystallins were isolated and characterized from sharks of the cartilaginous fishes. Four crystallin fractions corresponding to alpha-, beta H-, beta L- and gamma-crystallins, similar to those of mammalian crystallins, were obtained. The native molecular masses and subunit structures of these purified fractions were analyzed by gel permeation chromatography, SDS gel electrophoresis and isoelectric focusing, revealing the typical subunit compositions with various extents of heterogeneity in each orthologous crystallin class. Amino acid and N-terminal sequence analyses corroborate the identification and classification of crystallin classes based on electrophoresis. Unexpectedly, it was found that the amino acid composition and N-terminal sequence of shark gamma-crystallin are more closely related to those of bovine than carp gamma-crystallin. This finding may have some bearing on the divergence and specification of gamma-crystallins between the phylogenetic lines of mammals and fishes.