Zinov'eva R D, Tomarev S I, Piatigorsky J
Izv Akad Nauk Ser Biol. 1994 Jul-Aug(4):566-76.
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.
头足类动物和脊椎动物的晶状体是趋同进化的经典例子。在进化过程中，脊椎动物和头足类动物采用了相同的策略，即招募祖先蛋白质（主要是酶，其活性与应激和解毒有关）用于晶状体的结构功能。晶状体蛋白被定义为形成头足类动物和脊椎动物晶状体的水溶性蛋白质。在脊椎动物中，只有β/γ晶状体蛋白基因是晶状体特异性的。其他晶状体蛋白类别（α-、β-等）在晶状体中过度表达，在其他组织中也有不同程度的显著表达。几乎所有构成鱿鱼晶状体的晶状体蛋白都属于单一类别，即S-晶状体蛋白。后者由一个基因家族编码，该家族至少有10个成员。鱿鱼和章鱼的S-晶状体蛋白相关，但与谷胱甘肽S-转移酶不同。S-晶状体蛋白没有酶活性，尽管它们与我们已进行结构表征的鱿鱼谷胱甘肽-S-转移酶（GST）有42-44%的同源性。GST和S-晶状体蛋白的基因具有相似的外显子-内含子结构（5-6个外显子），而它们的5'侧翼区域不同。S-晶状体蛋白基因和一些脊椎动物晶状体蛋白基因的启动子都带有相似的调控元件（AP1位点），该元件必定参与它们晶状体特异性表达的调控。除了S-晶状体蛋白外，章鱼晶状体还含有一种主要的多肽，即ω-晶状体蛋白，已对其进行了详细表征。尽管ω-晶状体蛋白与醛脱氢酶（ALDG）相关，但它没有酶活性。编码ω-和S-晶状体蛋白的基因仅在鱿鱼和章鱼的晶状体细胞中表达。在一些哺乳动物中，已知ALDG可作为一种晶状体蛋白（象鼩的η-晶状体蛋白）。因此，章鱼的ω-晶状体蛋白和象鼩的η-晶状体蛋白是脊椎动物和头足类动物晶状体蛋白相似性的首个例子。
