Recombinant Human Relaxin-3 Protein

Human Relaxin-3 (H3 relaxin, INSL7) is one of seven relaxin-like peptides belonging to the insulin superfamily (1 - 4). Unlike human relaxins 1 and 2, it does not play a role in reproduction but appears to be a neuropeptide involved in stress response in the brain stem (3 - 5). The 142 amino acid (aa) Relaxin-3 pre-proprotein is processed to remove a 25 aa signal peptide and a connecting peptide (aa 53 - 118). The resulting mature Relaxin-3 is a 5.5 kDa, 51 aa secreted heterodimer of A (aa 119 - 142) and B (aa 26 - 52) peptides connected by two intermolecular disulfide bonds (1). Mature human Relaxin-3 is 96%, 94%, and 92% aa identical to porcine, canine, and mouse Relaxin-3, respectively. This is much higher identity between species than that seen for other relaxins. Relaxin-3 is thus suggested to be the ancestral relaxin family member (2). Relaxin-3 is the only known ligand for the G-protein-coupled receptor GPCR135, designated RXFP3 (4, 6). In rodents, GPCR135 is expressed primarily in the supraoptic and paraventricular nucleus (6). This region has connections to the dorsal tegmental region of the pons (also called the nucleus incertus), where expression of Relaxin-3 is highest (5). Relaxin-3 also binds the more widely-expressed LGR7 (RXFP1) receptor, but with lower affinity than that of Relaxin-2 (1, 7). Although binding of Relaxin-3 to LGR7 increases intracellular cAMP, binding to GPCR135 inhibits cAMP accumulation, indicating coupling to G_i, G_o or G_z by this receptor (1, 5). Relaxin-3 expression does not overlap well with its other receptor, GPCR142, which instead appears to be the primary receptor for INSL5 (3, 8).