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The peptide KLLLLKLLLLKLLLLKLLLLK, commonly referred to as KL4 peptide, is a synthetic 21-amino-acid cationic amphipathic peptide composed of repeating KLLLL motifs. The peptide was originally designed as a simplified pulmonary surfactant peptide that mimics key biophysical features of surfactant protein B (SP-B), including alternating positively charged lysine residues and strongly hydrophobic leucine-rich segments.
KL4 has been widely studied in pulmonary surfactant research because its lysine and leucine patterns promote interaction with lipid membranes. Published biophysical studies show that KL4 can associate with phospholipid monolayers and bilayers, insert into membrane environments, and influence surfactant film behavior at air–liquid interfaces. These properties make KL4 useful for studies of lung surfactant function, lipid–peptide interaction, and membrane-active peptide design.
Biological and Research Background
Pulmonary surfactant is a lipid–protein mixture that reduces surface tension in the alveoli and helps prevent alveolar collapse. Surfactant proteins such as SP-B and SP-C play important roles in organizing lipid films and promoting rapid spreading and respreading during breathing cycles. KL4 was developed as a synthetic peptide model that captures some of the lipid-interacting behavior of these surfactant-associated proteins while using a simple, reproducible sequence.
The KL4 sequence has also been used in synthetic surfactant systems. Sinapultide, also known as KL4 peptide, is a 21-residue peptide containing lysine and leucine residues and is used in lipid formulations designed to mimic human lung surfactant protein activity.
Applications in Pulmonary Surfactant Research
- Model peptide for pulmonary surfactant protein function
- Lipid monolayer and bilayer interaction studies
- Air–liquid interface and surface tension research
- Membrane insertion and amphipathic peptide studies
- Synthetic surfactant formulation development
Applications in Nucleic Acid and Pulmonary Delivery Research
In addition to surfactant research, KL4 has been investigated as a peptide-based carrier for pulmonary delivery of nucleic acids. Published work has reported that the synthetic KL4 peptide can form complexes with negatively charged nucleic acids and has been explored as an siRNA carrier for pulmonary delivery applications. More recent reviews of pulmonary nucleic acid delivery also describe KL4-based systems as promising platforms for lung-directed RNA delivery research.
- siRNA complexation and delivery studies
- mRNA pulmonary delivery formulation research
- Peptide-assisted nucleic acid delivery
- Lung-targeted non-viral delivery systems
- Dry-powder or aerosol-facing peptide formulation studies
Mechanistic Features
Amphipathic KL4 repeat design
The repeating KLLLL motif combines cationic lysine residues with hydrophobic leucine-rich segments. This arrangement supports lipid interaction and membrane association.
Lipid membrane insertion
KL4 has been studied for its ability to integrate into model lipid membranes and surfactant-like films, making it valuable for biophysical membrane studies.
Cationic nucleic acid interaction
The lysine residues provide a positive charge, allowing KL4 to interact with negatively charged nucleic acids, such as siRNA, under suitable formulation conditions.
Surfactant-mimetic behavior
KL4 is frequently used as a synthetic model for surfactant protein-inspired peptide design and surfactant replacement research.
Advantages of KL4 Peptide
- Defined 21-residue synthetic peptide sequence
- SP-B-inspired amphipathic lysine/leucine repeat design
- Strong lipid-interacting properties
- Useful for surfactant, membrane, and pulmonary delivery research
- Compatible with custom modifications, PEGylation, lipidation, or fluorescent labeling
Custom Modification Options
LifeTein can synthesize KL4 peptide with optional modifications for specialized research applications, including N-terminal acetylation, C-terminal amidation, fluorescent labeling, biotinylation, PEGylation, lipidation, isotope labeling, or conjugation to other biomolecules.
For CPP and peptide delivery-related formats, please also see our cell-permeable peptides / CPPs category and cell-penetrating peptide synthesis and conjugation page.
Research Use Only. Not for human or therapeutic use.
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