Recombinant Mouse Relaxin-1 Protein

Mouse Relaxin-1 (RLN1 or M1 relaxin) is the counterpart of human relaxin-2 (H2 relaxin) within the structurally related insulin/relaxin superfamily, while orthologs of the human relaxin-1 are found only in higher primates (1, 2). As with other insulin/relaxin superfamily members, RLN1 is synthesized as a preprohormone (1 ‑ 3, 5). Processing of the 21 kDa preprorelaxin-1 includes removal of the signal sequence, formation of two disulfide bonds between A and B chains and removal of the intervening C‑chain by a prohormone convertase. The resulting mature protein is an unglycosylated 6 kDa dimer of disulfide-linked A and B chains that binds the leucine-rich G-protein coupled receptor RXFP1, previously called LGR7 (1 ‑ 4). Mouse RLN1 shares only 67%, 39%, 36% and 42% amino acid (aa) identity with rat, equine and feline RLN1 and human Relaxin-2, respectively, and its activity shows partial species specificity. For example, a unique amino acid near the end of the A chain in mice, Tyr184, lowers its affinity for RXFP1 compared to other species (5). Mouse RLN1 is prominently expressed in the prostate and ovary, with lower levels in the brain, heart and other organs (1 ‑ 3). In the prostate, RLN1 is anti-apoptotic and contributes to development and maintenance of male fertility (6). In the female mouse, circulating RLN1 produced by the corpus luteum during pregnancy is essential for growth and softening of the cervix and vagina in preparation for delivery. It also promotes development of the mouse mammary apparatus, regulates plasma osmolality, and increases cardiac output and glomerular filtration rate in pregnancy (1, 2). Many RLN1 effects on reproductive tissues are augmented by estrogen (1 ‑ 3, 7). In non‑reproductive tissues, RLN1 mediates collagen turnover (7). RLN1-deficient mice develop age‑related fibrosis and smooth muscle hypertrophy in organs such as lung, heart, kidney and liver (7 ‑ 10).