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Updated: Aug 19, 2026
Production and Visualization of Bacterial Spheroplasts and Protoplasts to Characterize Antimicrobial Peptide Localization
Published on: August 11, 2018
Concentration-dependent realignment of the antimicrobial peptide PGLa in lipid membranes observed by solid-state
Ralf W Glaser1, Carsten Sachse, Ulrich H N Dürr
1Institute of Biochemistry and Biophysics, University of Jena, Jena, Germany.
Abstract:
The membrane-disruptive antimicrobial peptide PGLa is found to change its orientation in a dimyristoyl-phosphatidylcholine bilayer when its concentration is increased to biologically active levels. The alignment of the alpha-helix was determined by highly sensitive solid-state NMR measurements of (19)F dipolar couplings on CF(3)-labeled side chains, and supported by a nonperturbing (15)N label. At a low peptide/lipid ratio of 1:200 the amphiphilic peptide resides on the membrane surface in the so-called S-state, as expected. However, at high peptide concentration (>/=1:50 molar ratio) the helix axis changes its tilt angle from approximately 90 degrees to approximately 120 degrees , with the C-terminus pointing toward the bilayer interior. This tilted "T-state" represents a novel feature of antimicrobial peptides, which is distinct from a membrane-inserted I-state. At intermediate concentration, PGLa is in exchange between the S- and T-state in the timescale of the NMR experiment. In both states the peptide molecules undergo fast rotation around the membrane normal in liquid crystalline bilayers; hence, large peptide aggregates do not form. Very likely the obliquely tilted T-state represents an antiparallel dimer of PGLa that is formed in the membrane at increasing concentration.
Insights
Antimicrobial peptide PGLa shifts orientation in lipid bilayers at high concentrations. This peptide
Area of Science:
- Biophysics
- Membrane Biophysics
- Antimicrobial Peptides
Background:
- Antimicrobial peptides (AMPs) are crucial for innate immunity.
- PGLa is a well-studied membrane-disruptive AMP.
- Understanding AMP-membrane interactions is key to developing new therapeutics.
Purpose of the Study:
- To investigate the structural changes of PGLa within lipid bilayers at varying concentrations.
- To elucidate the orientation and aggregation state of PGLa in response to peptide/lipid ratios.
- To characterize the novel tilted T-state of PGLa.
Main Methods:
- Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
- Utilized (19)F and (15)N labeling for precise structural determination.
- Analyzed (19)F dipolar couplings and (15)N labeling to determine helix alignment.
Main Results:
- At low concentrations (1:200), PGLa adopts the surface-associated S-state.
- At high concentrations (>=1:50), PGLa transitions to a tilted T-state (approx. 120 degrees helix tilt).
- PGLa exists in an exchange between S- and T-states at intermediate concentrations, forming antiparallel dimers.
Conclusions:
- PGLa exhibits concentration-dependent conformational changes in lipid bilayers.
- The novel T-state represents a distinct orientation, potentially an antiparallel dimer.
- These findings offer new insights into AMP-membrane interactions and potential aggregation mechanisms.
