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 cryst allin in mammalian lenses, is structurally characterized in this study by cDNA cloning and sequencing. To facilitate sequence characterizati on of gamma S-crystallin possessing intermediate structural properties between beta- and gamma-crystallins, cDNA mixture was constructed hom the poly(A)(+) mRNA isolated from shark eye lenses, and amplification by polymerase chain reaction (PCR) was carried out to obtain nucleoti de segments encoding multiple shark gamma S-crystallins. Sequencing se veral 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 s pecies. Comparison of protein sequences encoded by two representative shark gamma S1 and gamma S2 cDNAs with those published sequences of be ta-, gamma-, and gamma S crystallins from bovine, human, bullfrog and carp lenses indicated that there is about 35-64% sequence homology bet ween shark gamma S crystallins and structurally related crystallins fr om different evolutionary classes, with a higher sequence similarity b etween shark gamma S and mammalian gamma-crystallins than that of shar k gamma S and carp gamma S or bovine gamma S crystallins. A phylogenet ic tree constructed on the basis of the sequence divergence among vari ous beta-, gamma-, and gamma S crystallins corroborates the closer rel atedness of shark gamma S to authentic gamma-crystallin than to mammal ian and teleostean gamma S crystallins. It further strengthens the sup position that ancestral precursors of gamma S-crystallins were present in the shark lens long before the appearance of present day teleostea n and mammalian gamma S-crystallins. (C) 1997 Academic Press.