Mouse relaxin: synthesis and biological activity of the first relaxin with an unusual crosslinking pattern

According to a recently published cDNA sequence, mouse relaxin has an extra amino acid in the C-terminal end of the A chain and thus an interchain loop consisting of 25 amino acids instead of the usual 24-membered ring. Because of the restrictive disulfide link arrangement the extra residue can be expected to cause a loop out in the C-terminal alpha-helix. We have chemically synthesized authentic mouse relaxin as well as an analog without the additional A chain residue and found that the native hormone, although active, was inferior to its insulin-like analog. This result is in harmony with our previous study which suggests that the surface of relaxin represented by the C-terminal helix of the A chain is positioned opposite to the surface that contains the receptor interaction site and therefore is less sensitive to modifications.