B7-33 Research Guide

Overview

B7-33 is a synthetic, single-chain 26-amino-acid peptide (sequence Val-Ile-Lys-Leu-Ser-Gly-Arg-Glu-Leu-Val-Arg-Ala-Gln-Ile-Ala-Ile-Ser-Gly-Met-Ser-Thr-Trp-Ser-Lys-Arg-Ser-Leu) engineered as an N-terminal truncated, C-terminal extended fragment of the B-chain of human relaxin-2 (H2 relaxin). Unlike native relaxin-2, which is a two-chain, disulfide-linked hormone, B7-33 is designed as a single, soluble peptide chain that retains the ability to engage the Relaxin Family Peptide Receptor 1 (RXFP1) while adopting a distinct receptor-engagement profile. Its molecular formula is approximately C₁₃₁H₂₂₉N₄₁O₃₆S, with a molecular weight of approximately 2,986.6 g/mol (CAS 1818415-56-3).

B7-33 was developed by researchers studying structure-activity relationships within the relaxin peptide family, with the goal of isolating a minimal peptide sequence capable of selectively activating a subset of RXFP1-linked intracellular signaling pathways. This guide focuses exclusively on published, laboratory-based research examining B7-33 pharmacology, signaling bias, and tissue-level effects in preclinical models, rather than on usage protocols. Available for research at Iron Peak Peptides: B7-33.

Within the broader relaxin research field, B7-33 is classified as a “biased agonist” — a ligand that, upon binding a single receptor, preferentially activates one downstream signaling cascade over another, in contrast to the full activation profile produced by the native hormone. This biased signaling property has made B7-33 a widely used tool compound in laboratory investigations of RXFP1 pharmacology, receptor-ligand structure-function relationships, and the cellular pathways implicated in fibrotic tissue remodeling.

Molecular Profile & Mechanism of Action

Structurally, B7-33 corresponds to the B-chain region of relaxin-2, the segment of the native hormone primarily responsible for RXFP1 receptor engagement, but omits the A-chain and associated disulfide bonds present in the full-length hormone. Published receptor pharmacology research has characterized B7-33 as a functionally selective, or “biased,” RXFP1 agonist: rather than activating the full complement of signaling pathways engaged by native relaxin-2 — which include both cyclic AMP (cAMP) accumulation and extracellular signal-regulated kinase (ERK1/2) phosphorylation — B7-33 has been shown in cell-based receptor assays to preferentially activate the phosphorylated ERK1/2 (pERK1/2) pathway with minimal engagement of the cAMP signaling arm (Hossain et al., 2016).

This biased activation profile is of particular research interest because the pERK1/2 pathway downstream of RXFP1 has been implicated in relaxin’s anti-fibrotic and tissue-remodeling effects observed in various animal and cell culture models, while cAMP-linked signaling has been more closely associated with relaxin’s vasodilatory and hemodynamic actions. By preferentially engaging one arm of RXFP1 signaling, B7-33 has served as a molecular tool for research groups seeking to dissect which specific intracellular pathways underlie particular tissue-level effects attributed to relaxin receptor activation, independent of the full native hormone’s broader signaling and structural complexity.

Follow-up structure-activity work has further explored single-chain relaxin mimetics, including lipidated derivatives designed to improve in vitro serum stability while preserving RXFP1 binding and functional activity, underscoring continued research interest in optimizing single-chain peptide scaffolds derived from the relaxin B-chain for use as pharmacological tools (Praveen et al., 2019; Praveen et al., 2023).

Published Research

Published research on B7-33 spans receptor pharmacology, cardiac tissue remodeling models, and pulmonary and renal fibrosis research, situating the peptide within a growing body of literature examining biased RXFP1 agonism as a research tool.

Hossain and colleagues first reported the design and synthesis of B7-33, describing its identification as a single-chain B-chain-only derivative of relaxin-2 capable of binding RXFP1 and functioning as a biased agonist with preferential activation of the pERK1/2 signaling pathway relative to cAMP accumulation, based on in vitro receptor binding and second-messenger assays (Hossain et al., 2016).

Devarakonda and colleagues investigated B7-33 in a mouse model of myocardial infarction, examining its effects on markers of adverse cardiac remodeling following induced infarction. The study reported that B7-33 administration was associated with attenuated indices of adverse structural remodeling in the post-infarction myocardium relative to untreated controls, consistent with a role for RXFP1-linked pERK1/2 signaling in modulating cardiac tissue remodeling processes after ischemic injury (Devarakonda et al., 2020).

Alam and colleagues compared B7-33 to the angiotensin-converting enzyme inhibitor perindopril in an experimental model of cardiomyopathy, reporting that B7-33 maintained cardioprotective effects comparable to those previously described for native relaxin and was associated with a more rapid reduction in left ventricular fibrosis markers in the study model relative to perindopril treatment over the observed time course (Alam et al., 2023).

Additional structure-activity research has examined single-chain relaxin receptor agonists more broadly, reviewing the pharmacological rationale for minimal peptide derivatives of relaxin such as B7-33 and describing ongoing efforts to develop lipidated or otherwise modified single-chain analogues with improved serum stability while preserving RXFP1 binding and pERK1/2-biased activity in vitro (Praveen et al., 2019; Praveen et al., 2023).

Taken together, this literature situates B7-33 as a widely referenced tool compound in relaxin receptor pharmacology research, with particular relevance to laboratory models of cardiac and broader fibrotic tissue remodeling, and as a scaffold for continued structure-activity optimization of single-chain RXFP1 agonists.

Chemical Properties & Specifications

• Common name: B7-33
• Chemical designation: Single-chain relaxin-2 (H2 relaxin) B-chain analogue peptide
• Peptide class: Relaxin Family Peptide Receptor 1 (RXFP1) biased agonist
• Amino acid sequence: Val-Ile-Lys-Leu-Ser-Gly-Arg-Glu-Leu-Val-Arg-Ala-Gln-Ile-Ala-Ile-Ser-Gly-Met-Ser-Thr-Trp-Ser-Lys-Arg-Ser-Leu
• Molecular formula: Approximately C₁₃₁H₂₂₉N₄₁O₃₆S
• Molecular weight: Approximately 2,986.6 g/mol
• CAS Number: 1818415-56-3
• Appearance: White to off-white lyophilized powder
• Storage: Store lyophilized peptide at -20°C, protected from moisture and light. Once reconstituted, solutions should be stored at 2-8°C and used within the timeframe established by the supplying laboratory; repeated freeze-thaw cycling should be avoided to preserve peptide integrity.

Research Applications

B7-33 is used in laboratory research primarily within the fields of receptor pharmacology, cardiovascular tissue biology, and fibrosis research. Specific research applications include in vitro RXFP1 binding and second-messenger assays used to characterize biased agonism and dissect the relative contributions of cAMP- and ERK1/2-linked signaling arms, as well as in vivo rodent models of myocardial infarction and cardiomyopathy used to examine downstream effects of RXFP1-biased signaling on markers of cardiac structural remodeling and fibrosis.

Researchers in the relaxin pharmacology field also study B7-33 as a template molecule for structure-activity relationship work, including the synthesis and evaluation of lipidated or otherwise chemically modified single-chain derivatives intended to improve in vitro serum stability while preserving receptor binding and functional bias. Additional research contexts include comparative pharmacology studies examining B7-33 alongside native relaxin-2 and other RXFP1 ligands, such as small-molecule allosteric agonists, to clarify how differences in receptor engagement translate into differences in downstream cellular signaling outcomes.

Given ongoing research interest in the molecular basis of tissue fibrosis across multiple organ systems, B7-33 continues to be examined as a tool compound for probing RXFP1-linked signaling pathways relevant to cardiac, pulmonary, and renal tissue remodeling models. Researchers frequently position B7-33 within a broader comparative framework of relaxin receptor pharmacology, alongside full-length relaxin-2 and other experimental RXFP1 ligands, when designing in vitro and in vivo research models intended to isolate specific receptor-signaling contributions to tissue-level outcomes.

References

1. Hossain MA, Kocan M, Yao ST, Royce SG, Nair VB, Siwek C, et al. (2016). A single-chain derivative of the relaxin hormone is a functionally selective agonist of the G protein-coupled receptor, RXFP1. Chemical Science.
2. Praveen P, Kocan M, Valkovic A, Bathgate R, Hossain MA. (2019). Single chain peptide agonists of relaxin receptors. Molecular and Cellular Endocrinology.
3. Devarakonda T, Mauro AG, Guzman G, Hovsepian S, Cain C, Das A, et al. (2020). B7-33, a Functionally Selective Relaxin Receptor 1 Agonist, Attenuates Myocardial Infarction-Related Adverse Cardiac Remodeling in Mice. Journal of the American Heart Association.
4. Alam F, Gaspari TA, Kemp-Harper BK, Low E, Aw A, Ferens D, et al. (2023). The single-chain relaxin mimetic, B7-33, maintains the cardioprotective effects of relaxin and more rapidly reduces left ventricular fibrosis compared to perindopril in an experimental model of cardiomyopathy. Biomedicine & Pharmacotherapy.
5. Praveen P, Wang C, Handley TNG, Wu H, Samuel CS, Bathgate RA, et al. (2023). A Lipidated Single-B-Chain Derivative of Relaxin Exhibits Improved In Vitro Serum Stability without Altering Activity. International Journal of Molecular Sciences.