New ribonuclease and ?,?-crystallin Homologs from Marine Organisms

The aim of the study was the production and haracterization of new homologs from two superfamilies of phylogenetic interest: the superfamily of ???-crystallin and that of RNases. Crystallins are proteins with key roles in lens function in vertebrates, but also extensively studied as models of molecular evolution. They have been studied in vertebrates as well as in unicellular organisms. Here, for the first time, a novel homolog from the earliest divergent metazoan, the Geodia cydonium sponge, has been isolated, both as a recombinant protein and from the natural source. The protein, named geodin, has been characterized in its main physico-chemical properties, including its behaviour with chemical denaturants, its thermal stability, and its stabilization with Ca2+ ions. Over one hundred homologs to bovine pancreatic RNase A have been isolated so far, and have constituted the “tetrapod RNase superfamily”. The isolation in this study of RNases from fish has led for the first time to the definition of a “vertebrate RNase superfamily”. The novel fish RNases, identified in the genome of zebrafish (Danio rerio), have been expressed as recombinant proteins and found to be active as RNA degrading enzymes, albeit poorly active. One of them has been found to be endowed with angiogenic activity, an activity found to be date only in mammalian RNases. These findings, and the positions of the three proteins in the RNase phylogenetic tree have led to the proposal that fish RNases might be ancestors to both tetrapod pancreatic-type RNases, as well as to mammalian angiogenins.