LL-37: Human Cathelicidin Antimicrobial Peptide Research Overview

Cathelicidins are a family of antimicrobial peptides produced as inactive proproteins that are cleaved by extracellular proteases to release the active C-terminal peptide. Humans produce only one cathelicidin, called hCAP18, which is cleaved to release the active 37-amino acid peptide LL-37 (named for its two N-terminal leucines).^[1]

LL-37 is produced by neutrophils, epithelial cells, and other immune cells as part of the innate immune defense system. The peptide has direct antimicrobial activity against a broad spectrum of pathogens (bacteria, fungi, some viruses) and also serves immunomodulatory roles independent of its direct microbial killing.^[2]

LL-37 is studied as a research reference compound in innate immunology and antimicrobial peptide pharmacology. It has not been approved by the FDA for any human therapeutic or medical purpose.

LL-37 structural features:

• Sequence: LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES (37 residues, one-letter code)

• Length: 37 amino acids

• Structure: amphipathic α-helix in membrane environments

• Net charge: +6 at physiological pH (multiple Arg and Lys residues)

• Molecular formula: C₂₀₅H₃₄₀N₆₀O₅₃

• Molecular weight: approximately 4,493 Da

When LL-37 binds bacterial membranes, it adopts an amphipathic α-helical structure with hydrophobic residues on one face and positively charged residues on the opposite face. This architecture allows the peptide to insert into negatively charged microbial membranes while sparing zwitterionic mammalian cell membranes.^[3]

The selectivity for microbial vs mammalian membranes derives from membrane composition: bacterial membranes have negatively charged phosphatidylglycerol and cardiolipin, while mammalian cell outer membranes are predominantly zwitterionic phosphatidylcholine.

LL-37's research-characterized activities span direct antimicrobial and immunomodulatory functions.

LL-37 binds negatively charged microbial membranes through electrostatic attraction, then inserts to form transmembrane pores or otherwise disrupt membrane integrity. This kills the microbe by leakage of cellular contents. The mechanism has been characterized in bacterial liposome systems and live bacteria preparations.^[3]

Beyond direct antimicrobial action, LL-37 binds the formyl peptide receptor 2 (FPR2) and other receptors on immune cells, modulating cytokine production, chemotaxis, and cell migration. This 'immunomodulatory' role is a major research area in modern cathelicidin biology.^[4]

Preclinical research has examined LL-37 in cell-based and animal models of wound healing, with endpoints including angiogenesis markers, keratinocyte migration, and re-epithelialization.^[5]

LL-37 literature spans innate immunity and applied antimicrobial research.

Cell-free liposome systems and live bacterial preparations are common substrates for LL-37 mechanism research. Endpoints include minimum inhibitory concentrations (MICs), bacterial membrane permeability assays, and structural studies of peptide-membrane interactions.^[3]

Cathelicidin expression has been examined in various cancer cell preparations. The peptide has dual reported effects in different tumor types — pro-tumorigenic in some contexts, anti-tumorigenic in others — reflecting the complexity of immunomodulatory signaling.^[6]

LL-37 dysregulation has been characterized in several inflammatory diseases including psoriasis (where LL-37 contributes to autoinflammatory signaling). Cell-based and skin preparation studies have examined the compound's role.^[4]

LL-37 is a large, highly charged peptide. Standard peptide handling applies.

Lyophilized LL-37 is stored at minus 20 degrees Celsius for long-term preservation.

Bacteriostatic water or sterile water are standard reconstitution solvents. The highly charged peptide is readily water-soluble.

HPLC for purity, mass spectrometry for identity confirmation matching the 37-amino acid sequence, and endotoxin screening. Each batch of Instant Peptides LL-37 ships with a full Certificate of Analysis.

Instant Peptides supplies LL-37 as a synthetic lyophilized reference compound. Material is supplied to qualified research professionals. Not for human or animal consumption.

View the product page for current pricing and the Certificate of Analysis for the active batch.