On the primary and tertiary structure of relaxin from the sand tiger shark ( Odontaspis taurus)

Abstract

The structural variability between the two known relaxin sequences from the pig [l-3] and rat [4] far exceed that observed for any insulin pair, yet their primary sequences can readily be folded into an insulin conformation [ 561. This raises the question of how much more variability in the primary sequence may be tolerated without preventing an insulin-like folding to occur and how much of the surface may be varied without loss of receptor interaction. The evolutionary diversion of relaxins from each other and the possible existence of a common ancestral gene for relaxins and insulinsled us to examine the structure of shark relaxin. Based on the assumption that sharks have existed in their present form for at least 500 million years, i.e., have lived close to the point at which fishes and the ancestors of mammals are assumed to have branched from each other and where the insulin gene might have undergone duplication to give rise to the relaxin gene, we expected to observe a closer relation between the relaxin of this quasi-prehistoric species and insulins.