GL13K is a short (13 amino acid) antimicrobial peptide derived from the parotid secretory protein. GL13K has been found to exhibit anti-inflammatory and antibacterial activities in physiological salt conditions. We investigated the mechanism of interaction of GL13K, with model membranes comprising 1, 2-dioleoylphosphatidylcholine (DOPC) and 1, 2-dioleoylphosphatidylglycerol (DOPG) using various biophysical and imaging techniques. Circular dichroism studies showed that GL13K adopts a β-sheet structure in the presence of negatively charged DOPG liposomes while it retains its random coil structure with zwitterionic DOPC liposomes. GL13K did not cause any fusion of these liposomes but was able to selectively disrupt the negatively charged membranes of DOPG leading to vesicular leakage. There was no or minimal evidence of GL13K interaction with DOPC liposomes, however an analysis of supported lipid bilayers (SLBs) using atomic force microscopic (AFM) imaging and dual polarization interferometry (DPI) suggested that GL13K can interact with the surface of a DOPC planar bilayer. In the case of DOPG bilayers, AFM and DPI clearly showed membrane thinned regions where a portion of lipid molecules has been removed. These results suggest that the mechanism of GL13K action on bacterial membranes involves localized removal of lipid from the membrane via peptide-induced micellization.
Bibliographical noteFunding Information:
The authors would like to acknowledge the Natural Science and Engineering Research Council of Canada (NSERC) , the Canadian Foundation for Innovation (CFI) and the Centre for Self Assembled Chemical Structures (CSACS) for financial support. Dr. László Kálmán and Dr. Jack Kornblatt are acknowledged for their contributions to discussions and assistance with DPI and ITC, respectively.
- Antimicrobial peptide
- Dual polarization interferometry
- Isothermal titration calorimetry
- Membrane disruption
- Model membrane
- Supported lipid bilayer: atomic force microscopy