Human Beta-Defensin 2

Chemical Identity

Property	Value
Chemical Formula	C182H280N52O54S8
Molecular Weight	4327.96 g/mol
CAS Number	159612-77-2
IUPAC Name	Beta-defensin 2 (DEFB4A gene product)
Peptide Class	Beta-Defensin
Disulfide Bonds	3 (stabilizing cysteine-stabilized motif)

Structure

Human beta-defensin 2 (hBD-2) is a 41-amino acid cationic peptide with three intramolecular disulfide bonds connecting Cys1-Cys5, Cys2-Cys4, and Cys3-Cys6 in a characteristic beta-defensin pattern. The peptide folds into a compact structure with an antiparallel beta-sheet stabilized by the disulfide network. Six positively charged residues (four arginines, two lysines) provide a net positive charge of +4 at physiological pH.

Mechanism of Action

hBD-2 disrupts microbial membranes through electrostatic interaction with negatively charged bacterial lipids, followed by membrane permeabilization:

• Direct killing: Primarily active against gram-negative bacteria (E. coli, P. aeruginosa) with lower activity against gram-positive organisms
• Membrane disruption: Forms multimeric pores in bacterial inner membranes
• Chemotaxis: Binds CCR6, recruiting immature dendritic cells and memory T cells to sites of infection
• Immune activation: Promotes mast cell degranulation and histamine release

Biological Functions

hBD-2 is an inducible defensin expressed primarily at mucosal epithelial surfaces:

• Expression sites: Skin keratinocytes, airway epithelium, gastrointestinal mucosa, oral epithelium
• Induction: Strongly upregulated by bacterial products (LPS, lipoteichoic acid), IL-1beta, TNF-alpha, and through TLR2/TLR1 signaling
• Role in inflammation: Part of the immediate innate immune response before adaptive immunity develops

Clinical Relevance

hBD-2 expression is altered in several disease states. Reduced expression in atopic dermatitis contributes to susceptibility to skin infections. In cystic fibrosis, defective hBD-2 processing may contribute to chronic lung infections. Polymorphisms in the DEFBA4 gene copy number are associated with susceptibility to psoriasis and Crohn’s disease. Therapeutic strategies to enhance endogenous hBD-2 production are under investigation.

Safety and Side Effects

As an endogenous human peptide, hBD-2 has minimal toxicity at physiological concentrations. Exogenous administration may cause local inflammation at high doses due to chemotactic activity. No systemic toxicity has been reported in preclinical studies.

References

• Harder, J., et al. (1997). A peptide antibiotic from human skin. Nature, 387, 861.
• Yang, D., et al. (1999). Beta-defensins: linking innate and adaptive immunity through dendritic and T cell CCR6. Science, 286, 525-528.