Research Only Healing & Recovery

KR-12

also known as: LL-37(18-29), KRIVQRIKDFLR, minimal LL-37 antimicrobial fragment

KRIVQRIKDFLR — the minimal 12-residue bactericidal fragment of LL-37. Retains selective antimicrobial activity while losing LL-37's host-cell toxicity, making it the canonical template for LL-37-derived antimicrobial peptide drug discovery. Research-only.

A 12-residue peptide corresponding to LL-37 residues 18–29 (Lys-Arg-Ile-Val-Gln-Arg-Ile-Lys-Asp-Phe-Leu-Arg), characterized by Guangshun Wang's group at the University of Nebraska Medical Center as the smallest LL-37 fragment that retains bactericidal activity against Escherichia coli while showing minimal hemolytic and cytotoxic activity against human erythrocytes and keratinocytes. KR-12 has become the canonical minimal LL-37 template for antimicrobial peptide drug discovery, with multiple groups producing chemically modified, D-amino-acid-substituted, and lipidated analogs intended to overcome the proteolytic-instability limitation of the native L-amino-acid peptide. Not FDA-approved; not in clinical development as a standalone agent.

Mechanism of action

Forms amphipathic α-helix on contact with negatively charged bacterial membrane lipids (particularly phosphatidylglycerol and cardiolipin), producing rapid membrane permeabilization through a carpet-or-toroidal-pore mechanism. The 12-residue size appears to be near the minimum for coherent amphipathic α-helix formation in a membrane environment. Selectivity for bacterial over mammalian membranes arises from the charge difference between bacterial (negatively charged) and mammalian (largely zwitterionic) outer-leaflet phospholipids. Also retains weak LPS-neutralizing activity of the parent LL-37.

Primary uses

Antimicrobial peptide research (in vitro and preclinical)
Template for LL-37-derived antibiotic drug discovery
Wound-healing biomaterial research (peptide-functionalized hydrogels and dressings)

Typical dosing

Not established for human use

⚠ No human dosing established. Topical preclinical studies have used μM-to-mM concentrations. Any human use would be unregulated.

Regulatory status

Native KR-12 is not FDA-approved. Various KR-12 derivatives and analogs are in preclinical and early-clinical development for topical antimicrobial and wound-healing applications, but no KR-12-based agent has entered a registered Phase 2 or later clinical trial as of early 2026.

References

[pubmed] Wang G. "Structures of human host defense cathelicidin LL-37 and its smallest antimicrobial peptide KR-12 in lipid micelles." J Biol Chem, 2008;283:32637-32643 (KR-12 minimal-fragment characterization).
[pubmed] Mishra B, Wang G. "Ab initio design of potent anti-MRSA peptides based on database filtering technology." J Am Chem Soc, 2012;134:12426-12429.
[review] Wang G, Narayana JL, et al. "Human antimicrobial peptides and proteins." Pharmaceuticals (Basel), 2014;7:545-594.

Related peptides

LL-37

The only human cathelicidin — an antimicrobial peptide with direct activity against bacteria, fungi, viruses, and biofilms, with additional roles in wound healing and immune signaling.

FK-13

The 13-residue FKRIVQRIKDFLR central fragment of LL-37 — the smallest LL-37 fragment that retains broad-spectrum antimicrobial activity while losing much of the parent peptide's cytotoxicity toward mammalian cells. Research-only; no clinical development program.

Disclaimer

This entry is for educational purposes only and does not constitute medical advice. Dosing information reflects published regulatory or research data and is not a recommendation. Many compounds described here are not approved for human use in the United States. Consult a licensed medical professional before considering any peptide therapy.