Structure-function analysis of Avian β-defensin-6 and β-defensin-12: role of charge and disulfide bridges

• Published in: BMC microbiology Vol. 16; no. 1; p. 210
• Main Authors: Yang, Ming, Zhang, Chunye, Zhang, Xuehan, Zhang, Michael Z., Rottinghaus, George E., Zhang, Shuping
• Format: Journal Article
• Language: English
• Published: England BioMed Central 09.09.2016
• Subjects: Amino Acid Sequence; Animals; Anti-Bacterial Agents - pharmacology; Anti-Infective Agents - pharmacology; Antibiotics; Antimicrobial agents; Bacteria; Bacterial Load; Bacterial Proteins; beta-Defensins - chemistry; beta-Defensins - genetics; beta-Defensins - pharmacology; beta-Defensins - physiology; beta-Lactamases - metabolism; Cell Culture Techniques; Cell Line; Cell Survival; Chemotaxis - drug effects; Chickens; Cricetinae; Dendritic Cells - immunology; Disulfides - chemistry; DNA, Bacterial; E coli; Escherichia coli - drug effects; Genome, Bacterial; Kinetics; Klebsiella pneumoniae - drug effects; Lipopolysaccharides - metabolism; Macrophages - drug effects; Mice; Microbial Sensitivity Tests; Microscopy, Electron, Transmission; Neutralization Tests; Pathogens; Peptides; Peptides - chemistry; Peptides - pharmacology; Peptides - physiology; Receptors, Chemokine; Salmonella; Salmonella typhimurium - cytology; Salmonella typhimurium - drug effects; Salmonella typhimurium - genetics; Sodium chloride; Sodium Chloride - chemistry; Staphylococcus aureus - drug effects; Avian β-defensins; Antimicrobial activity; Chemotactic activity; LPS-neutralizing activity; Net positive charge; Disulfide bridges
• ISSN: 1471-2180; 1471-2180
• DOI: 10.1186/s12866-016-0828-y

Avian beta-defensins (AvBD) are small, cationic, antimicrobial peptides. The potential application of AvBDs as alternatives to antibiotics has been the subject of interest. However, the mechanisms of action remain to be fully understood. The present study characterized the structure-function relationship of AvBD-6 and AvBD-12, two peptides with different net positive charges, similar hydrophobicity and distinct tissue expression profiles. AvBD-6 was more potent than AvBD-12 against E. coli, S. Typhimurium, and S. aureus as well as clinical isolates of extended spectrum beta lactamase (ESBL)-positive E. coli and K. pneumoniae. AvBD-6 was more effective than AvBD-12 in neutralizing LPS and interacting with bacterial genomic DNA. Increasing bacterial concentration from 10(5) CFU/ml to 10(9) CFU/ml abolished AvBDs' antimicrobial activity. Increasing NaCl concentration significantly inhibited AvBDs' antimicrobial activity, but not the LPS-neutralizing function. Both AvBDs were mildly chemotactic for chicken macrophages and strongly chemotactic for CHO-K1 cells expressing chicken chemokine receptor 2 (CCR2). AvBD-12 at higher concentrations also induced chemotactic migration of murine immature dendritic cells (DCs). Disruption of disulfide bridges abolished AvBDs' chemotactic activity. Neither AvBDs was toxic to CHO-K1, macrophages, or DCs. AvBDs are potent antimicrobial peptides under low-salt conditions, effective LPS-neutralizing agents, and broad-spectrum chemoattractant peptides. Their antimicrobial activity is positively correlated with the peptides' net positive charges, inversely correlated with NaCl concentration and bacterial concentration, and minimally dependent on intramolecular disulfide bridges. In contrast, their chemotactic property requires the presence of intramolecular disulfide bridges. Data from the present study provide a theoretical basis for the design of AvBD-based therapeutic and immunomodulatory agents.