Alpha-Defensin (HNP-1)

Alpha-defensin HNP-1 (Human Neutrophil Peptide-1) is a cationic antimicrobial peptide stored in azurophilic granules of neutrophils and released during degranulation to kill phagocytosed microorganisms. It is one of the most abundant proteins in neutrophils, comprising approximately 5-7% of total neutrophil protein.

The 30-amino acid peptide contains six cysteine residues forming three intramolecular disulfide bonds in a characteristic defensin fold. This constrained structure creates an amphipathic molecule with cationic and hydrophobic surfaces that enables interaction with and disruption of microbial membranes.

HNP-1 demonstrates broad-spectrum antimicrobial activity against gram-positive and gram-negative bacteria, fungi, and some enveloped viruses. The mechanism involves electrostatic attraction to negatively charged microbial membranes, followed by insertion and pore formation that disrupts membrane integrity and osmotic balance.

Beyond direct antimicrobial activity, alpha-defensins function as immunomodulators, influencing chemotaxis, cytokine production, and adaptive immune responses. Elevated plasma levels of HNP-1 serve as biomarkers for neutrophil activation in infection, inflammation, and certain malignancies, making defensins valuable in both basic research and diagnostic applications.