Stress-response research fragment (CRF[22-41; I19])

What this is

CRF[22-41; I19] is a synthetic 20-residue fragment derived from corticotropin-releasing factor (CRF), the hypothalamic peptide that initiates the body's stress response. The fragment covers positions 22 through 41 of the full-length CRF sequence, with an isoleucine substitution at position 19 of the parent peptide — the "[I19]" designation in the name refers to that single-residue change, which is reflected in the stored sequence here. Because this fragment lacks the N-terminal region of CRF that is responsible for activating the CRHR1 receptor, it is used as a research tool to probe the biology of the second CRF receptor subtype, CRHR2, which has a distinct tissue distribution and functional profile from CRHR1. Patthy and colleagues (1986, PNAS) characterized a family of CRF-related polypeptides isolated from porcine hypothalami that stimulated corticotropin release from rat pituitary cells, establishing that truncated CRF fragments retain biological activity and providing early structural context for the fragment series to which this peptide belongs.

What it does

CRF acts through two receptor subtypes — CRHR1, which is the primary driver of the classical stress axis in the pituitary and is widely expressed in the brain, and CRHR2, which has a more restricted distribution including the heart, skeletal muscle, and specific brain regions associated with appetite regulation and stress recovery. Fragments spanning the C-terminal half of CRF, including the [22-41] region, preferentially engage CRHR2 over CRHR1, making them useful probes for separating the two receptor-mediated pathways in preclinical settings. CRF[22-41; I19] is used in research as a selective CRHR2 ligand to investigate the receptor's roles in anxiolytic signaling, cardiovascular protection, and appetite suppression — all areas where CRHR2 activity has been implicated in contrast to the predominantly anxiogenic, stress-activating profile of CRHR1.

Evidence

• Human: No human clinical trials on CRF[22-41; I19] are published or registered. This peptide is a research tool, not a clinical candidate.
• Animal: The parent CRF fragment series was characterized in rat pituitary preparations by Patthy and colleagues (1986), who isolated structurally related porcine hypothalamic polypeptides and demonstrated their corticotropin-releasing activity. CRHR2-selective CRF analogs spanning the C-terminal region have been studied in preclinical models probing cardiovascular, anxiolytic, and feeding-behavior pathways; this specific analog is used as a pharmacological tool in that body of work.
• In vitro: Binding selectivity for CRHR2 versus CRHR1 has been assessed in receptor-expression systems as part of the broader characterization of C-terminal CRF fragment pharmacology.

Mechanism

CRF and its analogs bind class B G-protein-coupled receptors (GPCRs). CRHR1 and CRHR2 are both class B GPCRs that couple primarily through Gαs, elevating intracellular cAMP. The two receptors differ in their N-terminal extracellular domain, which forms the major ligand-binding surface; the N-terminal region of CRF (roughly residues 1–21) contributes critically to CRHR1 binding and activation, while the C-terminal region (residues 22–41) is sufficient for CRHR2 engagement. CRF[22-41; I19] lacks the full CRHR1-activating N-terminus, giving it selectivity toward CRHR2. CRHR2 is expressed in cardiac muscle, the dorsal raphe, and hypothalamic nuclei linked to energy homeostasis, which explains the receptor's association with cardioprotective, anxiolytic, and anorexigenic effects distinct from the HPA-axis-activating, anxiogenic profile driven by CRHR1.

Related peptides

• The full-length CRF sequence is the parent from which this fragment is derived; CRF[22-41; I19] retains the C-terminal pharmacophore while losing the CRHR1-activating N-terminus.
• Urocortins (Ucn1, Ucn2/stresscopin-related peptide, Ucn3/stresscopin) are endogenous mammalian CRF-family peptides with varying CRHR1/CRHR2 selectivity; Ucn2 and Ucn3 are selective for CRHR2, sharing overlapping biology with what CRF[22-41; I19] is used to probe.