Squid major lens polypeptides are homologous to glutathione S-transferases subunits

Abstract

The eye lenses of cephalopods and vertebrates evolved relatively recently and by independent routes¹. They provide a good experimental model for the study of convergent evolution at the protein level. One proposal is that pre-existing proteins were recruited as structural eye lens proteins during evolution². This has been confirmed for the vertebrate eye lens structural proteins, or crystal-lins^3–9, which have been intensively studied^10,11. Despite the limited information about cephalopod eye Ienses^12–14, it has been suggested that glutathionine S-transf erases (GSTs) are a possible evolutionary ancestor of the squid major lens proteins. Recently, the N-terminal sequence of the squid major lens protein was shown³ to be 55% homologous with that of the Ya subunit of the rat GST. Here, we demonstrate that the squid major lens polypeptides are encoded by a gene family of at least three members. We characterize two cDNAs corresponding to these genes and show they probably either are GST subunits themselves, or share an evolutionary ancestor with them.