Recombinant Human Relaxin-2 (B-29/A-24) Protein

Human Relaxin-2, also called H2 Relaxin, is a 6 kDa, 53 amino acid (aa) nonglycosylated, heterodimeric polypeptide that plays an important role in female reproduction (1, 2). Relaxin belongs to a structurally related insulin/relaxin superfamily that currently contains 10 members in human (2). To date, three human relaxin genes have been identified (1, 2). Among these, Relaxin-2 is best studied and the only known Relaxin to circulate in the blood (2, 3). As with other insulin/relaxin superfamily members, human Relaxin-2 is synthesized as a preprohormone (4). It is 18 kDa in size and 185 aa in length. It contains a 24 aa signal sequence, a 3.3 kDa, 31 aa B domain, a 106 aa C (or connecting) domain, and a C-terminal, 2.7 kDa, 24 aa A domain (2, 4, 5). Upon removal of the signal peptide, two intrachain disulfide bonds are created between the B and A chains. This is followed by prohormone convertase removal of the intervening C-chain, creating a disulfide-linked heterodimer. Initially, the B chain is 31 aa in length and terminates with a Lys‑Arg dipeptide. This is subsequently cleaved by a carboxypeptidase to generate a 29 aa mature chain (5). The mature human Relaxin-2 heterodimer is 48%, 44% and 43% aa identical to rat, canine and porcine Relaxin-2, respectively. Human Relaxin‑2 is 35% and 75% aa identical to human Relaxin-3 and 1, respectively. An alternate splice form for human Relaxin-2 has been reported (6). It is identical to the standard form through the first 70 aa of the preproprecursor. At this point, a 47 aa substitution occurs that appears to be absent in typical cleavage motifs. Relaxin confers its activity by binding to leucine-rich guanine nucleotide-binding (G-protein) coupled receptors, LGR7 and LGR8 (2, 7). Relaxin is best known as a hormone of parturition that promotes growth and softening of the cervix, and development of the mammary gland (2, 3). It also has a marked impact on the uterus. In particular, it promotes angiogenesis, inhibits MMP production and activity, and down‑regulates estrogen receptor‑ alpha expression (8).