Structure-function analysis of Avian β-defensin-6 and β-defensin-12: role of charge and disulfide bridgesReport as inadecuate

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BMC Microbiology

, 16:210

Microbe-host interactions and microbial pathogenicity


BackgroundAvian 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.

ResultsAvBD-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 CFU-ml to 10 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.

ConclusionsAvBDs 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.

KeywordsAvian β-defensins Antimicrobial activity LPS-neutralizing activity Chemotactic activity Net positive charge Disulfide bridges Abbreviations4-CN4-Chloro-1-Naphthol

AAAmino acid

ANOVAOne-way analysis of variance

AvBDAvian beta-defensin

BSABovine serum albumin

C.I.Chemotaxis index

CDCircular dichroism

CFUColony-forming unit

DCsDendritic cells

FBSFetal bovine serum



GFPGreen fluorescent protein

GM-CSFGranulocyte macrophage colony-stimulating factor

HRPHorseradish peroxidase




LTALipoteichoic acid

MICMinimum inhibitory concentration

NADPHNicotinamide adenine dinucleotide phosphate

PBSPhosphate buffered saline

RP-HPLCReversed-phase high performance liquid chromatography

SDStandard deviation

TEMTransmission electron microscopy

TLR4Toll-like receptor 4


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Author: Ming Yang - Chunye Zhang - Xuehan Zhang - Michael Z. Zhang - George E. Rottinghaus - Shuping Zhang


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