LL-37 is a 37-amino-acid peptide derived from the C-terminal region of hCAP18, the only cathelicidin identified in humans. It is named for its two N-terminal leucine residues and its length. In basic research, LL-37 is one of the most studied host defense peptides, used to investigate how cationic amphipathic peptides interact with membranes and how innate immune signaling is modulated in cell models. This overview covers LL-37 as a laboratory reagent.
Structure of LL-37
LL-37 begins with the sequence LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES. In aqueous solution it is largely unstructured, but in the presence of membranes or certain ions it folds into an amphipathic alpha-helix, with hydrophobic residues on one face and cationic residues on the other. That conformational switch is central to how it is studied.
The molecular weight is approximately 4,493 Da. At 37 residues, synthesis can generate closely related deletion sequences, so a lot should be backed by both HPLC purity and a mass spectrum showing the correct parent mass.
The Cathelicidin Family
Cathelicidins are a family of host defense peptides found across many vertebrates, each stored as an inactive precursor and released by proteolytic cleavage. LL-37 is the mature human form. Comparative research often contrasts it with cathelicidins from other species, or with shorter LL-37 fragments such as KR-12, to determine which regions of the sequence drive specific activities in vitro.
Common Laboratory Research Themes
- Membrane interaction: studying how LL-37 associates with and disrupts model lipid bilayers.
- Microbiology assays: measuring activity against bacterial cultures in vitro.
- Innate immune signaling: examining effects on toll-like receptor and chemokine pathways in cultured cells.
- Biofilm models: characterizing interaction with bacterial biofilms in laboratory systems.
- Fragment mapping: comparing full-length LL-37 with truncated variants.
These are preclinical research applications. Results obtained in culture or model membrane systems describe behavior in those systems only.
LL-37 Specifications at a Glance
- Class: cathelicidin host defense peptide
- Length: 37 amino acids
- Form: lyophilized powder
- Verification: HPLC purity and mass spectrometry identity, third-party tested
Quality Documentation for LL-37
For any LL-37 lot, the most useful document is the Certificate of Analysis. A credible COA identifies the lot number, the analytical method used for purity (typically reversed-phase HPLC with UV detection), the observed molecular mass from mass spectrometry, and the date of testing. If you are new to this, our guide on how to read a peptide Certificate of Analysis walks through each field, and our explainer on HPLC and mass spectrometry purity testing covers why the two methods are complementary.
Genetic Peptides USA lots are independently tested through PepAssure third-party verification, so the identity and purity numbers on the label can be traced back to a specific batch. Researchers comparing suppliers should confirm that the COA lot matches the vial lot, that the mass spectrum is consistent with the theoretical mass, and that purity is reported as a chromatographic area percentage rather than an unexplained single number.
Storage and Stability Considerations
LL-37 is supplied as a lyophilized (freeze-dried) powder. In that form, peptides are generally most stable when kept cold, dry, and protected from light, and repeated temperature cycling should be avoided. Once a lyophilized peptide is brought into solution for an assay, stability characteristics change, so many labs prepare only what a given experiment requires and document preparation dates carefully. Our article on lyophilized peptide handling and storage covers general laboratory practices for freeze-dried research materials.
Where to Go Next
Review lot details on our LL-37 research peptide page or browse the Immune and Gut Research collection. For another short peptide studied in inflammation-signaling models, see the KPV research peptide overview.
Frequently Asked Questions
What is LL-37?
LL-37 is a 37-amino-acid peptide cleaved from hCAP18, the human cathelicidin, and is one of the most studied host defense peptides in laboratory research.
Why does LL-37 structure change in membranes?
LL-37 is largely unstructured in water but folds into an amphipathic alpha-helix in the presence of lipid membranes, which is central to how it is studied in vitro.
What is LL-37 studied for in the lab?
Research uses include membrane interaction studies, in-vitro microbiology and biofilm assays, and innate immune signaling in cultured cells.
What molecular weight should an LL-37 COA show?
An observed mass consistent with approximately 4,493 Da, plus HPLC purity and a lot number matching the vial.
Is this product for human or animal use?
No. It is supplied for laboratory research use only and is not for human or veterinary use. It is not a drug, food, or cosmetic and is not intended to diagnose, treat, cure, or prevent any disease.
All products referenced in this article are sold strictly for laboratory research use only. They are not for human or veterinary use, are not drugs, foods, or cosmetics, and are not intended to diagnose, treat, cure, or prevent any disease. Nothing here is guidance on administration or handling outside a qualified laboratory setting.