Human Neutrophil Peptide 1

Alpha-defensins including HNP-1 adopt a triple-stranded antiparallel beta-sheet structure stabilized by three disulfide bonds. This folded structure creates a facially amphipathic beta-sheet that inserts into bacterial membranes. Unlike alpha-helical AMPs, HNP-1 disrupts membranes through a mechanism involving dimerization at the membrane surface, lateral compression of the lipid bilayer, and pore formation. The cis-disulfide orientation of alpha-defensins distinguishes them from beta-defensins which have the trans configuration.

HNP-1 inhibits HIV-1 and HIV-2 at micromolar concentrations through multiple mechanisms: direct viral membrane disruption, CXCR4 co-receptor blocking (competing with gp120), and intracellular inhibition of reverse transcriptase. Beyond direct antiviral effects, HNP-1 recruits dendritic cells and T cells through chemokine receptor interactions, linking innate AMP activity to adaptive immune activation. This immunomodulatory function is relevant to vaccine adjuvant applications.

HNP-1 shows MIC values of 1-10 ug/mL against Staphylococcus aureus, Streptococcus pyogenes, E. coli, P. aeruginosa, and Candida albicans. Activity is salt-sensitive (reduced at physiological NaCl), which limits potency in extracellular fluids but not in the low-salt phagosome where HNP-1 kills engulfed bacteria. This phagosomal mechanism is the primary physiological antibacterial role.

Serum HNP-1-3 concentrations are elevated in sepsis, HIV infection, bacterial infections, and inflammatory bowel disease, reflecting neutrophil degranulation. HNP-1 levels correlate with disease severity in sepsis and may have prognostic value. Locally elevated HNP-1 in saliva correlates with oral bacterial burden, and in BAL fluid with lung infection severity. While not a drug target currently, HNP-1 levels are studied as diagnostic and prognostic biomarkers.