Octopus S-crystallins with endogenous glutathione S-transferase (GST) activity: sequence comparison and evolutionary relationships with authentic GST enzymes.
S-Crystallin is a major protein present in the lenses of cephalopods (octopus and squid). To facilitate the cloning of this crystallin gene, cDNA was constructed from the poly(A)+ mRNA of octopus lenses, and amplified by PCR for nucleotide sequencing. Sequencing of 10 of 15 positive clones coding for this crystallin revealed three distinct S-crystallin isoforms with 61-64% identity in nucleotide sequences and 42-58% similarity in amino acid sequences when compared with homologous crystallins in squid lenses. These charge-isomeric crystallins also show between 26 and 33% amino acid sequence identity to four major classes of glutathione S-transferase (GST), a major detoxification enzyme present in most mammalian tissues. For further analysis, expression of one of the S-crystallin cDNAs was carried out in the bacterial expression system pQE-30, and the S-crystallin protein produced in Escherichia coli was purified to homogeneity to determine the enzymic properties. We found that the expressed octopus S-crystallin possessed much lower GST activity than the authentic GSTs from other tissues. Sequence comparison and construction of phylogenetic trees for S-crystallins from squid and octopus lenses and various classes of GSTs revealed that S-crystallins represent a multigene family which is structurally related to Alpha-class GSTs and probably derived from the ancestral GST by gene duplication and subsequent multiple mutational substitutions.
Chiou
S H
SH
Laboratory of Crystallin Research, National Taiwan University, Taipei.
Yu
C W
CW
Lin
C W
CW
Pan
F M
FM
Lu
S F
SF
Lee
H J
HJ
Chang
G G
GG
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D003459:Crystallins / Q000235:genetics / Q000378:metabolism*; D018076:DNA, Complementary; D049832:Decapodiformes; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D049831:Octopodiformes; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
D003459:Crystallins; D018076:DNA, Complementary; D005982:Glutathione Transferase