Structural insights into the action of relaxin peptide hormones

Introduction The human relaxin family of peptide hormones comprises seven members: H1, H2 and H3 relaxin and the insulin-like peptides INSL3-6. These hormones play a number of distinct physiological roles, many of which are yet to be characterized, but they all have the common structural characteristics of two peptide chains that are folded tightly together into a compact globular fold that is stabilized by three disulfide bonds (Fig. 1).