LEAP-1, a novel highly disulfide-bonded human peptide, exhibits antimicrobial activity Original paper

What was studied?

This original research article characterized LEAP-1 (liver-expressed antimicrobial peptide), a newly identified human antimicrobial peptide discovered in human blood ultrafiltrate using a mass spectrometry–based assay optimized for cysteine-rich peptides. The investigators isolated a 25–amino acid peptide with eight cysteine residues forming four disulfide bonds, an unusually dense disulfide motif in human peptides, and confirmed its structure by Edman sequencing plus mass shifts after reduction and alkylation. They then synthesized LEAP-1, oxidized it to achieve the fully disulfide-bonded form, and demonstrated that synthetic and native peptides co-eluted and matched by electrophoresis, supporting correct folding. Finally, they tested antimicrobial activity via radial diffusion assays and colony-forming unit (CFU) killing assays, and cloned the corresponding cDNA to define the precursor protein and expression pattern across tissues by real-time RT-PCR.

Who was studied?

The biological “subjects” were human-derived samples and human tissues, plus microbial test organisms. LEAP-1 was isolated from human blood ultrafiltrate (plasma-derived peptide filtrate). For gene expression, the authors analyzed cDNA panels from 14 human tissues, showing the strongest expression in the liver with lower expression elsewhere. For functional testing, LEAP-1 was challenged against a set of Gram-positive bacteria (Bacillus megaterium, Bacillus subtilis, Micrococcus luteus, Staphylococcus carnosus), a Gram-negative bacterium (Neisseria cinerea), and yeast (Saccharomyces cerevisiae); additional organisms (E. coli BL21, Pseudomonas fluorescens, Rhodotorula rubra) were tested and found resistant.

Most important findings

LEAP-1 emerged as a highly disulfide-bonded, cationic antimicrobial peptide with a striking tissue signature: predominant liver expression, unlike many antimicrobial peptides that are primarily epithelial or neutrophil-derived. Structurally, LEAP-1 contains four disulfide bonds within a 17–residue stretch, a unique feature in the known human proteome, and it is produced as part of an 84–amino acid secretory precursor containing a signal peptide and a polybasic (penta-arginine) processing site, consistent with regulated secretion and proteolytic maturation. Functionally, LEAP-1 displayed dose-dependent antimicrobial activity, with strongest susceptibility among Gram-positive organisms and measurable activity against N. cinerea and S. cerevisiae. In CFU assays, half-maximal inhibitory concentrations were approximately 40 µg/mL (14.4 µM) for B. subtilis and 50 µg/mL (18 µM) for S. cerevisiae, placing it in the same order of magnitude as other known antimicrobial peptides. Importantly for a microbiome signatures database, LEAP-1’s spectrum suggests selective pressure particularly on Firmicutes-like Gram-positive taxa while sparing certain Proteobacteria (e.g., E. coli, Pseudomonas), implying it could shape microbial ecology in niches exposed to liver-derived factors (e.g., portal circulation, biliary interfaces) or systemic inflammatory states. The tissue expression figure underscores liver dominance, with comparatively elevated signal also reported in heart and brain relative to many other tissues, raising the possibility of organ-specific antimicrobial or immunomodulatory roles beyond barrier defense.

Key implications

Clinically, LEAP-1 provides an early blueprint for how the host can deploy liver-biased antimicrobial peptides as part of systemic innate immunity, potentially linking hepatic immune sensing to downstream microbial control. For microbiome translation, the study supports modeling LEAP-1 as a host factor that may preferentially suppress select Gram-positive taxa and yeast while leaving some Gram-negative commensals/pathobionts unaffected—an asymmetry that could matter in liver disease, sepsis, or inflammatory states where hepatic peptide output changes. The authors explicitly note that extrapolating in vitro potency to in vivo effects is difficult because local concentrations, inflammatory induction, and synergy with other immune components likely determine real-world impact; nonetheless, the unusual expression pattern suggests LEAP-1 could participate in liver-specific immune programs, including interactions with acute-phase pathways. As a database signature, “high LEAP-1 expression + susceptibility pattern” could be tracked alongside microbial shifts in conditions involving hepatic inflammation or altered portal exposure, offering a mechanistic bridge between host peptide biology and observed microbiome community changes.

Citation

Krause A, Neitz S, Mägert HJ, et al. LEAP-1, a novel highly disulfide-bonded human peptide, exhibits antimicrobial activity. FEBS Lett. 2000;480(2-3):147-150