LL-37

LL-37 Peptide Overview

LL-37 is a high-purity, laboratory-synthesized peptide that precisely replicates the molecular structure of the only known human cathelicidin antimicrobial peptide. Composed of 37 amino acids, this peptide is characterized by its unique N-terminal sequence beginning with two leucine residues, which provides the basis for its nomenclature as "LL-37." In biological systems, LL-37 is liberated from the C-terminus of the precursor protein hCAP-18 through specialized enzymatic cleavage. It is naturally expressed in epithelial tissues and various circulating immune cells. Current scientific inquiry focuses on the peptide’s multifaceted roles in antimicrobial defense, immunomodulation, and tissue regeneration within strictly controlled experimental and preclinical environments.

LL-37 Peptide Structure

The structural integrity of LL-37 is fundamental to its biological utility. It is a cationic, amphipathic alpha-helical peptide, a configuration that allows it to interact dynamically with both lipid membranes and various cellular receptors.

Molecular Specifications:

• Amino Acid Count: 37 residues
• Sequence: LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES
• Molecular Formula: C205H340N60O53
• Molecular Weight: 4493.3 g/mol

Property

Specification

Physical Appearance

Lyophilized White Powder

Peptide Purity

Greater than 98 percent

Solubility

Water Soluble

Source

Chemical Synthesis

Net Charge

+6 at physiological pH

LL-37 Peptide Research

LL-37 and Inflammatory Conditions

While LL-37 is recognized for its defensive capabilities, research has identified its presence in several complex inflammatory pathways, including those associated with psoriasis, lupus, rheumatoid arthritis, and atherosclerosis. The behavior of the peptide is highly context-dependent, varying significantly based on the local inflammatory environment and the specific cell types involved.

Experimental data suggests that LL-37 can mitigate keratinocyte apoptosis and modulate the production of interferon-alpha. Furthermore, it has been observed to influence the migration of neutrophils and eosinophils while suppressing signaling through toll-like receptor 4. These findings indicate that LL-37 acts as a homeostatic regulator, attempting to stabilize immune activity and prevent runaway inflammation during systemic stress. Recent evidence suggests that elevated levels of LL-37 in autoimmune contexts may represent a protective response by the body to restore balance rather than a driver of the disease itself.

LL-37 as a Potent Antimicrobial Agent

As a cornerstone of the innate immune system, LL-37 serves as a primary defense against pathogens. In healthy skin, LL-37 levels are generally low but escalate rapidly upon the detection of invading microorganisms. The peptide exhibits broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, and certain enveloped viruses.

The mechanism of action is largely attributed to its interaction with bacterial lipopolysaccharide (LPS). By binding to LPS, LL-37 disrupts the stability of the bacterial outer membrane, leading to membrane permeabilization. Additionally, LL-37 has been shown to work in synergy with other molecules, such as human beta-defensin 2 and lysozyme, to amplify the overall efficacy of the host's antimicrobial response.

LL-37 and Respiratory Health

The presence of LPS is not limited to bacterial infections; it is also found in airborne contaminants like mold and fungi. Inhalation of these particles triggers LL-37 production in lung tissue. Research is currently investigating the potential of exogenous LL-37 as a therapeutic model for managing lung inflammation related to toxic dust syndrome, asthma, and COPD.

Beyond defense, LL-37 appears to promote respiratory tissue repair. It stimulates the proliferation and migration of airway epithelial cells, facilitating the closure of wounds and the restoration of damaged tissue. By promoting angiogenesis, LL-37 supports the growth of new blood vessels necessary for supplying nutrients to regenerating lung segments.

Understanding LL-37 in Arthritis

In studies involving rheumatoid arthritis, researchers have noted significant concentrations of LL-37 within synovial joints. While earlier theories questioned if the peptide contributed to joint degradation, current evidence points toward a protective role. Animal models lacking the LL-37 gene show no improvement in arthritic symptoms, suggesting the peptide is a byproduct of the inflammation rather than the cause.

Furthermore, LL-37 and its derived analogs have demonstrated the ability to protect against collagen degradation. In laboratory settings, the administration of LL-37 peptides to inflamed joints resulted in a reduction of disease severity and a decrease in serum antibodies against type II collagen. This indicates that LL-37 may selectively mitigate joint inflammation by interacting with receptors such as TLR3 and TLR4.

LL-37 and Intestinal Health

Research using intestinal cell cultures shows that LL-37 supports the integrity of the intestinal barrier by promoting epithelial cell migration and reducing programmed cell death. These protective qualities suggest potential utility in studying inflammatory bowel diseases and recovery from intestinal surgery.

LL-37 works alongside human beta-defensin 2 to restore epithelial integrity and mitigate damage caused by TNF-alpha. Because current treatments for intestinal inflammation often carry risks of systemic infection, LL-37-based research offers a pathway toward developing targeted modulators that maintain gut health without compromising the broader immune system.

LL-37 and Intestinal Cancer

Investigations into the relationship between LL-37 and oncology have revealed promising results in the context of gastric and intestinal cancers. The peptide appears to exert anti-tumor effects through a vitamin D-dependent mechanism. Research suggests that vitamin D enhances the ability of macrophages to combat tumors specifically by upregulating LL-37, highlighting a synergistic pathway that may contribute to reduced gastrointestinal cancer risks.

LL-37 and Blood Vessel Formation

LL-37 influences the production of prostaglandin E2 (PGE2) in endothelial cells. While PGE2 is often associated with inflammatory pain, it is also a critical driver of angiogenesis. The ability of LL-37 to modulate the formation of new blood vessels makes it a vital subject of study for wound healing, stroke recovery, and the management of cardiovascular health.

Ongoing LL-37 Research

The structural divergence of LL-37 between humans and other mammals provides a unique opportunity for biophysical study. Even when sharing core sequences, the three-dimensional folding of the peptide determines its specific receptor binding and biological impact. This makes LL-37 an essential model for understanding protein engineering and the design of targeted therapeutic peptides.

While LL-37 demonstrates high subcutaneous bioavailability in animal models, it is important to note that dosing and physiological effects observed in laboratory animals do not translate directly to human applications.

Article Author

This review was compiled, edited, and organized by Dr. Ayyalusamy Ramamoorthy, Ph.D. Dr. Ramamoorthy is a distinguished biophysical chemist renowned for his extensive research on antimicrobial peptides. His work has been pivotal in defining the structural biology of LL-37, providing the scientific community with a deeper understanding of how this peptide interacts with lipid bilayers and immune receptors to facilitate tissue repair and pathogen clearance.

Scientific Journal Author

Dr. Ayyalusamy Ramamoorthy, Professor of Biophysics and Chemistry at the University of Michigan, has authored several landmark publications, including "LL-37, the only human cathelicidin: structure, function, and applications" (Biochim Biophys Acta, 2006). His collaborations with researchers like Dr. Robert E.W. Hancock and Dr. Judith M. Kahlenberg have established a comprehensive foundation for the study of cathelicidins in modern medicine.

Reference Citations

1. Durr UH, Sudheendra US, Ramamoorthy A. LL-37, the only human cathelicidin: structure, function, and applications. Biochim Biophys Acta. 2006;1758(9):1408-1425.
2. Vandamme D, et al. A comprehensive summary of LL-37 and its derived peptides. Cell Mol Life Sci. 2012;69(20): 3885-3908.
3. Nijnik A, Hancock RE. The roles of cathelicidin LL-37 in immune defences and novel clinical applications. Curr Opin Hematol. 2009;16(1):41-47.
4. Overhage J, et al. Human host defense peptide LL-37 prevents bacterial biofilm formation. Infect Immun. 2008;76(9):4176-4182.
5. Heilborn JD, et al. The cathelicidin peptide LL-37 is involved in re-epithelialization of human skin wounds and is lacking in chronic ulcers. J Invest Dermatol. 2003;120(3):379-389.
6. Barlow PG, et al. Antiviral activity and increased host defense response of LL-37 in influenza virus infection. J Immunol. 2011;186(10): 6166-6174.
7. Kahlenberg JM, Kaplan MJ. Little peptide, big effects: the role of LL-37 in inflammation and autoimmune disease. J Immunol. 2013;191(10):4895-4901.
8. Mookherjee N, et al. Modulation of the TLR-mediated inflammatory response by LL-37. J Immunol. 2006;176(4):2455-2464.
9. Krasnodembskaya A, et al. Human cathelicidin peptide LL-37 promotes mesenchymal stem cell-mediated immunomodulation and tissue repair. Proc Natl Acad Sci USA. 2010;107(32):14292-14297.
10. Ramos R, et al. Wound healing activity of LL-37 peptide. Peptides. 2011;32(9):1849-1858.

Storage

Storage Instructions

All LL-37 peptide products are manufactured via lyophilization (freeze-drying), a process that ensures molecular stability during transit for 3 to 4 months. Lyophilization involves freezing the peptide and reducing surrounding pressure to allow the frozen water to sublimate directly from a solid to a gas. This leaves a stable, crystalline powder.

Upon arrival, the lyophilized peptide should be stored in a cool, dark environment. For immediate research needs, refrigeration at 4 degrees Celsius is sufficient. For long-term preservation (months to years), the peptide should be kept in a freezer at -80 degrees Celsius.

Best Practices For Storing Peptides

Proper handling is vital to prevent degradation, oxidation, and contamination.

• Reconstitution: Once the peptide is reconstituted with bacteriostatic water, it must be refrigerated and used within 30 days.
• Temperature Consistency: Avoid frost-free freezers, as temperature cycles during the defrost phase can damage the peptide’s structural integrity.
• Contamination Prevention: Always allow the vial to reach room temperature before opening to prevent moisture condensation inside the container.

Preventing Oxidation and Moisture Contamination

To protect the peptide from air exposure, keep the container sealed whenever possible. Researchers may use an inert gas like nitrogen or argon to blanket the peptide before sealing to prevent oxidation. Dividing the peptide into smaller aliquots for individual experiments is recommended to avoid repeated freeze-thaw cycles.

Storing Peptides In Solution

Peptide solutions are less stable than their lyophilized counterparts. If a solution must be stored, use a sterile buffer with a pH between 5 and 6. Aliquoting is essential here to minimize temperature fluctuations. While refrigerated solutions can last up to 30 days, any peptide not intended for immediate use should remain in its lyophilized state.

Peptide Storage Containers

High-quality glass vials are preferred for their chemical inertness and clarity. However, polypropylene plastic vials are often used for shipping to prevent breakage. Researchers may transfer the product between containers as needed, provided the new container is clean, sterile, and chemically resistant.