Human neutrophil peptide 1 variants bearing arginine modified cationic side chains: effects on membrane partitioning

Area of Science:

• Biochemistry
• Immunology
• Microbiology

Background:

• Alpha-defensins (e.g., human neutrophil peptides, HNPs) are crucial components of innate immunity with broad-spectrum bactericidal activity.
• The interaction of cationic antimicrobial peptides with negatively charged bacterial membranes is initiated by positively charged amino acid side chains.
• Alpha-defensins possess a higher proportion of arginine (Arg) residues than lysine (Lys) residues.

Purpose of the Study:

• To investigate the role of the Arg guanidino group and the localized cationic charge of Lys in the interaction of α-defensins with lipid membranes.
• To evaluate the impact of specific Arg substitutions on the membrane disruptive activity of α-defensins.

Main Methods:

• Synthesis and study of α-defensin analogs with substitutions at position 14 (and 15) of Arg.
• Variants included substitutions with N(G)-N(G')-asymmetric dimethyl-l-arginine (ADMA), N(G)-N(G')-symmetric dimethyl-l-arginine (SDMA), and Lys.
• Analysis of membrane partitioning and disruptive activity of native HNP-1 and its variants.

Main Results:

• All studied variants exhibited decreased disruptive activity against lipid bilayers compared to native HNP-1.
• Methylated Arg analogs (ADMA, SDMA) showed reduced membrane partitioning, attributed to their inability to form hydrogen bonds.
• Lysine substitution variants (R14K, R15KR14KR15K) also displayed diminished membrane interaction.

Conclusions:

• The specific cationic charge provided by arginine residues, particularly the guanidino group, is critical for effective membrane interaction and antimicrobial activity of α-defensins.
• Modifications that alter the charge distribution or hydrogen bonding capacity of these residues significantly impair peptide function.
• These findings underscore the precise structural requirements for α-defensin-membrane interactions in innate immunity.