Recombinant Human Relaxin R1 Fc Chimera Protein, CF

Relaxin R1 (Relaxin receptor 1), also known as RXFP1 (Relaxin family peptide receptor 1) or LGR7 (leucine‑rich G‑protein‑coupled receptor 7) is a member of family C of the LGRs, and is one of four receptors for Relaxin family proteins. Relaxin R1 shows highest affinity for human Relaxins 1, 2 and 3, while RXFP2 binds Relaxin 2 and the related INSL3, and RXFP3 primarily binds Relaxin 3 (1, 2). The 757 amino acid (aa) human Relaxin R1 contains an N‑terminal 409 aa extracellular domain (ECD) with a calcium‑binding LDL R class A (LDLa) domain and 10 leucine‑rich repeats (LRR) with several N‑glycosylation sites. The C‑terminus contains 12 transmembrane domains within aa 410‑672. Human Relaxin R1 (aa 1‑398) shares 84, 86, 85, 85 and 91% aa sequence identity with mouse, rat, equine, bovine and porcine Relaxin R1, respectively. Isoforms of 724 and 709 aa lack aa 63‑96 and 300‑348, respectively, while isoforms of 176, 189, 191 and 337 aa diverge after aa 154, 179, 181 and 324, respectively (3, 4). These forms may dimerize with full‑length Relaxin R1 and reduce its expression on the cell surface (3, 4). Receptor activation and cAMP signaling depend on the LDLa domain, and Relaxin binding requires the LRR repeats, with a secondary binding site within transmembrane region exoloops (1, 2, 5). Of LGR family members, RXFP1 and RXFP2 are unique in that they are not internalized to down‑regulate signaling, and their LDLa domains allow transmission of both G‑protein‑dependent and ‑independent signals (1, 2, 6, 7). Engagement of Relaxin R1 by Relaxin (mainly Relaxin 2 in humans) supports female reproduction by promoting uterine angiogenesis, ovarian follicle ripening, and endometrial, cervical and nipple development (8‑10). In male reproduction, Relaxin R1 acts in the prostate to enhance sperm motility (11). It reduces fibrosis in the heart, skin, lungs, liver, kidney, and reproductive tissues by combating aberrant collagen buildup (12). In the vasculature, it mediates vasodilation and decreases blood pressure. Relaxin R1 is expressed on human leukocytes and promotes adhesion, migration, and osteoclast differentiation (13, 14). Additional effects on heart, lungs, kidney and brain are reported, some of which may be species‑specific (1).