Human β-defensin 4 - defensin without the "twist"

Area of Science:

• Immunology
• Structural Biology
• Antimicrobial Peptides

Background:

• Beta-defensins (β-defensins) are crucial cationic peptides in innate and adaptive immunity, exhibiting broad-spectrum antimicrobial activity.
• Some human β-defensins (hBDs) modulate immune cell migration by targeting chemokine receptors like CCR2 and CCR6.
• While ~50 human β-defensin genes exist, only hBD1-3 are well-characterized; limited data exists for hBD4 and hBD6.

Purpose of the Study:

• To elucidate the crystal structure of human beta-defensin 4 (hBD4).
• To investigate the potential for unique dimerization of hBD4.
• To assess the functional activity of hBD4 regarding chemokine receptor CCR6 and its antimicrobial properties.

Main Methods:

• X-ray crystallography was employed to determine the structure of hBD4 at 1.60 Å resolution.
• Solution studies, including analytical ultracentrifugation, were used to confirm potential dimerization.
• Functional assays were performed to evaluate hBD4's chemotactic activity on CCR6-expressing cells and its bactericidal efficacy against E. coli.

Main Results:

• The crystal structure of hBD4 revealed significant structural differences compared to other known β-defensins.
• Evidence suggested a unique dimerization capability for hBD4 in solution.
• hBD4 demonstrated potent antibacterial activity against E. coli but did not induce CCR6-mediated chemotaxis, attributed to its N-terminal conformation.

Conclusions:

• hBD4 possesses distinct structural features, including potential unique dimerization, differentiating it from previously characterized β-defensins.
• The unusual N-terminal conformation of hBD4 explains its lack of CCR6-mediated chemotactic activity.
• hBD4 remains a potent antimicrobial agent, highlighting its role in host defense despite differing receptor interactions.