Molecular Behavior of Human β Defensin Type 3 Embedded in Different Model Lipid Membranes

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Human β defensin type 3 (hBD-3) is a potent antimicrobial peptide (AMP) with potential to combat drug resistance.
• hBD-3 exhibits unique functionality in high salt concentrations, unlike many other AMPs.
• The precise molecular mechanism of hBD-3's membrane interaction and disruption remains poorly understood.

Purpose of the Study:

• To elucidate the molecular structure and dynamics of hBD-3 during membrane interaction and crossing.
• To investigate the influence of disulfide bonds, salt concentration, and membrane composition on hBD-3 behavior.
• To differentiate the membrane-crossing mechanisms of wild-type hBD-3 and its analog lacking disulfide bonds.

Main Methods:

• Extensive all-atom molecular dynamics simulations (57.0 μs) were performed on hBD-3 monomers and dimers.
• Simulations included wild-type and analog (disulfide-bond-free) forms in four distinct lipid membrane environments.
• Conformational dynamics analysis, including contact matrices, principal component analysis (PCA), and linear discriminant analysis (LDA), was employed for trajectory analysis.

Main Results:

• The primary structural distinction observed was between the wild-type and analog forms of hBD-3.
• The analog monomer showed significant structural degradation without disulfide bonds; salt had a consistent effect, while membrane composition had minimal impact.
• The hBD-3 dimer displayed no clear structure-salt relationship, and membrane composition had limited influence on its dynamics. The dimer could differentiate between Gram-positive and Gram-negative membranes, unlike the monomer.

Conclusions:

• Wild-type and analog hBD-3 likely utilize different mechanisms for bacterial membrane translocation.
• The high net charge density of hBD-3 may mitigate the effects of salt on its dynamics.
• hBD-3 dimers possess a greater capacity than monomers to discriminate between different bacterial membrane types, offering insights into targeted antimicrobial strategies.