Molecular Structure Explorer
LL-37
Structure of the compound covered in this guide.
Last reviewed: October 2026 · Cleared Peptides research team
Research use only. LL-37: Research Guide to the Human Cathelicidin Peptide is supplied for laboratory research. It is not a drug, food, cosmetic, or dietary supplement. It is not FDA-approved. It is not for human or veterinary administration. This page does not give a dose or a method of administration. A study cited on this page describes that study’s own test article. It does not make this lot an approved medicine. To check a fact, open the PubMed or DOI link, confirm the authors and year, and match the paper’s compound name, CAS number, or sequence to the specification table. The full method is on the research desk page. Identity and purity for a lot are only what that lot’s certificate of analysis reports. An HPLC percentage is not a sterility result and not an endotoxin result unless the certificate prints those tests.
LL-37 is the 37-amino-acid active peptide released from human cathelicidin (hCAP18) and the only cathelicidin found in humans. Its name comes from its two N-terminal leucines and its length. It is a reference antimicrobial peptide in membrane biophysics and innate-immunity research.
LL-37 Structure and Identifiers
| Name | LL-37 |
|---|---|
| Synonyms | Human cathelicidin antimicrobial peptide |
| CAS number | 154947-66-7 |
| PubChem CID | 16198951 |
| Molecular formula | C205H340N60O53 |
| Molecular weight | ≈4493.3 g/mol |
| Sequence | LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES |
| Form | Lyophilized powder |
Structure and Membrane Interaction
LL-37 is cationic (net charge ≈ +6) and amphipathic, forming an α-helix in membrane-like environments. It interacts preferentially with negatively charged bacterial membranes, which is the basis of membrane-disruption and selectivity studies.
Published In-Vitro Research Areas
- Antimicrobial and anti-biofilm assays
- Lipid-membrane biophysics
- Innate-immunity signaling (TLR modulation, chemotaxis)
- Peptide aggregation and oligomerization
This summary describes laboratory research only and makes no claim about effects in humans or animals.
Purity Testing and Storage
Every lot of LL-37 supplied by Cleared Peptides is tested by an independent laboratory for identity and purity (or composition, for multi-component preparations), and the lot Certificate of Analysis is published on our COA page. Store lyophilized LL-37 at −20 °C, sealed, dry and protected from light. Allow the vial to reach room temperature before opening and minimize freeze–thaw cycles. Handle according to your institution’s chemical-hygiene procedures.
Analytical testing notes for LL-37
LL-37 is identified in this guide as CAS 154947-66-7, formula C205H340N60O53, listed mass ≈4493.3 g/mol. The sequence recorded here is LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES. An identity test compares a measurement with those values. A mass spectrum is the usual measurement for a peptide. FTIR, when a certificate uses it, is a supporting infrared fingerprint and is less specific for closely related sequences.
For LL-37, routine chemical characterization is reversed-phase HPLC for area-percent purity and mass spectrometry for identity against the formula and mass in the table above. Oxidizable residues (cysteine, methionine, tryptophan) and deamidating residues (asparagine, glutamine), when the sequence contains them, are typical related-impurity questions for the chromatogram and the mass spectrum.
HPLC purity for this material is an area-percent result at the wavelength and gradient the laboratory states, commonly ultraviolet detection near 214 nm on a reversed-phase column. The instrument is a gradient pump, injector, column oven, and UV or diode-array detector. That percentage is not the number of milligrams in the vial. Water, acetate, trifluoroacetate, and other UV-silent material can dominate the gross weight while the purity figure stays high. Net peptide content, from an assay or amino-acid analysis, is the separate result to read when the certificate reports it.
A sterility test and an endotoxin test are not included in a chemical purity result. The compendial sterility test is a culture method (USP <71>): membrane filtration or direct inoculation into fluid thioglycollate medium and soybean-casein digest medium, incubated for 14 days. A PCR sterility screen uses a thermal cycler to detect microbial DNA and is a different method. The endotoxin test (USP <85> LAL, or USP <86> recombinant Factor C) reports endotoxin units with an incubating reader or a cartridge reader. Use a result only when that method is printed on the lot certificate. One published example in this catalog states that the report does not cover microbial contamination or endotoxins. The full description of equipment, standards, and how US laboratory accreditation works is in peptide analytical testing. Lot records are on the COA page.
Frequently Asked Questions
What does LL-37 stand for?
It refers to the peptide’s two N-terminal leucines (LL) and its 37-residue length.
Is LL-37 for human use?
No. Cleared Peptides supplies LL-37 for laboratory research use only; it is not for human or veterinary use.
Written by the Cleared Peptides Research Desk, the editorial desk of Cleared Wellness Group LLC. This is not a personal profile of a physician or a scientist, and it is not a fictional author. The checking method is public on the research desk page. Last reviewed October 2026.
LL-37 research note: the mature human cathelicidin peptide
Research use only. This LL-37 material is for laboratory research, CAS 154947-66-7. It is not an antibiotic drug, and an antimicrobial result in a paper is not a sterility test of this vial. This page does not give a dose or a method of administration.
Gene, precursor, mature peptide
Gudmundsson, Agerberth, Odeberg, and colleagues (European Journal of Biochemistry, 1996) characterized FALL39, the only cathelicidin gene they found in the human genome. Exons 1–3 encode the signal and the cathelin region. Exon 4 encodes the mature antibacterial peptide. They isolated that mature peptide from granulocytes. The precursor is longer than the peptide. A mass for hCAP-18, the precursor, does not confirm LL-37, and the reverse is also true. PubMed 8681941, DOI 10.1111/j.1432-1033.1996.0325z.x.
Dürr, Sudheendra, and Ramamoorthy (Biochimica et Biophysica Acta, 2006) review LL-37 as the only human cathelicidin peptide: 37 residues, amphipathic helix, discussed both as an antimicrobial peptide and as a modulator of innate immune cells. The review is biophysical and immunological background. It is not a certificate. PubMed 16716248, DOI 10.1016/j.bbamem.2006.03.030.
The catalog sequence is LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, formula C205H340N60O53, mass about 4493.3 g/mol. The name LL-37 is the first two residues plus the length. A truncated analogue that still begins with Leu-Leu is a different mass. The sequence is strongly basic, so it binds surfaces and anionic lipids. That physical fact is why handling and chromatography are fussier than for a neutral short peptide. It is also why a microbiology zone-of-inhibition result, in a paper that used a defined bacterial strain, cannot be copied onto a chemical purity certificate.
How to verify this note
- Open Gudmundsson 1996 and confirm the mature peptide was isolated from granulocytes and is encoded by exon 4 of FALL39.
- Match the 37-residue sequence and CAS 154947-66-7. Count residues if a supplier’s sequence is shorter.
- Treat antimicrobial activity as a result inside the paper that measured it. Sterility of this lot, if it was tested, is a separate line on the certificate.
Selected References
Peer-reviewed literature on the compounds discussed in this guide, listed as scientific background for laboratory researchers. Citation does not imply endorsement by the authors or any use other than in-vitro research.
- Bucki R, et al. Cathelicidin LL-37: a multitask antimicrobial peptide. Arch Immunol Ther Exp (Warsz). 2010;58(1):15-25. PubMed 20049649 · DOI
- Verjans ET, et al. Molecular mechanisms of LL-37-induced receptor activation: An overview. Peptides. 2016;85:16-26. PubMed 27609777 · DOI
Laboratory note: solubility depends on salt form and solvent. This guide does not state a single solubility figure. Handling of lyophilized material is described in the peptide storage guide.
Research Use Only Notice
This guide is provided for educational and laboratory reference purposes. It summarizes published, primarily in-vitro and structural research literature and does not describe, recommend or imply any use in humans or animals. Products sold by Cleared Peptides are for laboratory research use only; they are not drugs, foods, cosmetics or dietary supplements, are not FDA-approved, and are not intended to diagnose, treat, cure, mitigate or prevent any disease. No dosing, administration or therapeutic information is provided.
