Yes, Relaxin is a Peptide That Starts with "R"
Relaxin is a well-characterized peptide hormone that begins with the letter R and belongs to the insulin superfamily of peptides. 1
Relaxin Family Peptides
The relaxin family comprises multiple peptides, several of which start with "R":
- Relaxin (H2 relaxin/RLN2): The primary circulating form in humans, produced by the corpus luteum during pregnancy 1
- H1 relaxin (RLN1): A human-specific form encoded by a separate gene 1
- Relaxin-3 (H3 relaxin/RLN3): Present in humans, rats, and mice, primarily expressed in the brain 1
Structural Characteristics
Relaxin is a 6-kDa polypeptide hormone with the following features:
- Two-chain structure: Consists of separate A and B chains connected by disulfide bonds, similar to insulin 1, 2
- Conserved receptor-binding motif: Contains the sequence Arg-X-X-X-Arg-X-X-Ile/Val on the B chain, which is highly conserved across species despite significant sequence variation elsewhere in the molecule 1, 2
- Molecular weight: Approximately 6000 daltons 2, 3
Receptor Interactions
Relaxin peptides bind to specific G-protein coupled receptors:
- RXFP1 (formerly LGR7): Primary receptor for H2 relaxin, with binding affinity order of H2 relaxin > H1 relaxin > H3 relaxin > INSL3 1
- RXFP3 (formerly GPCR135): Receptor for H3 relaxin (relaxin-3) 1
Physiological Roles
Relaxin functions as a reproductive hormone with multiple actions: