At least seven relaxin-like proteins make up the Insulin/Relaxin superfamily. Most consist of two peptide subunits, an alpha-chain and a beta-chain, linked by disulfide bonds. Relaxin-3, also known as INSL7, has been reported as a ligand for LGR7 (RXFP1), and is the only known ligand for GPCR135 (RXFP3). It binds less often with GPCR142. Relaxin-3 is a secreted protein that is reported to play a role in stress response. It is almost exclusively expressed within the brain stem.