[The evolutionary kinship of the crystallins of cephalopods and vertebrates with heat-shock proteins and stress-induced proteins].

The lenses of cephalopods and vertebrates are a classical example of convergent evolution. In the course of evolution vertebrates and cephalopods used the same strategy of recruitment of ancestral proteins (primarily enzymes, whose activity is related with stress and detoxification) for structural functions in the lens. Crystallins are defined as water soluble proteins, that form the lenses of cephalopods and vertebrates. In vertebrates, only the beta/gamma-crystallin genes are lens-specific. The other crystallin classes (alpha-, beta-, etc) are overexpressed in the lens, having the various noticeable expression levels in the other tissues as well. Almost all the crystallins, forming squid lens are referred to a single class, namely S-crystallins. The latters are encoded by a family of genes, consisting of at least 10 members S-crystallins of the squid and the octopus are related, but not identical to glutathione S-transferases. S-crystallins show no enzymatic activity, though they have 42-44% homology with a squid glutathione-S-transferase (GST), which we have structurally characterized. Genes of GST and S-crystallins have similar exon-intron structures (5-6 exons), whereas their 5' flanking regions are different. Promoters of both of S-crystallin genes and of some vertebrate crystallin genes bear the similar regulatory element (AP1-site), that must take part in regulation of their lens-specific expression. Besides S-crystallins, octopus lens contains a major polypeptide, omega-crystallin, that was characterized in detail. Though omega-crystallin is related to aldehyde dehydrogenase (ALDG), it has no enzymatic activity. Genes coding for omega- and S-crystallins were shown to be expressed only in the lens cells of squid and octopus. In some mammals ALDG is known to serve as a crystallin (eta-crystallin of elephant shrew). Thus, octopus omega-crystallin and eta-crystallin of elephant shrew--are the first example of similarity between vertebrate and cephalopod crystallins.