Conformational studies of vasopressin and mesotocin using NMR spectroscopy and molecular modelling methods. Part I: Studies in water.

Arginine vasopressin (AVP) and mesotocin (MT) belong to the neurohypophyseal hormone family. The former plays a very important role in the control of urine concentration and the blood pressure in mammals, whereas the latter stimulates uterine concentration and initiates birth in amphibians, marsupials, wallabies, birds, and fishes. Analysis of their 3D structure could be helpful for understanding the evolutionary relationship between all vasopressin- and oxytocin-like hormones. In addition, it allows design of new analogs with appropriate biological activity for humans and animals. In this paper, we present the conformational studies of AVP and MT, under the aqueous conditions. In our investigations, we used 2D NMR spectroscopy and time-averaged molecular dynamics calculations in explicit water. Our studies have shown that both peptides, despite displaying a high sequence homology, differ from each other with regard to the three-dimensional structure. They are in conformational equilibrium as a result of the cis/trans isomerization across the Cys(6)-Pro(7) peptide bond. Both peptides form beta-turns in their cyclic part, wherein the C-terminal fragment of MT is bent, whereas that of AVP is extended.