| AVS 63rd International Symposium & Exhibition | |
| Biomaterial Interfaces | Monday Sessions |
| Session BI+AS-MoM |
| Session: | Biomolecules and Cells at Interfaces |
| Presenter: | Thaddeus Golbek, Oregon State University |
| Authors: | T.W. Golbek, Oregon State University J. Franz, Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, Mainz, Germany J.E. Fowler, Oregon State University K.F. Schilke, Oregon State University T. Weidner, Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, Mainz, Germany J.E. Baio, Oregon State University |
| Correspondent: | Click to Email |
Cationic amphiphilic peptides have been engineered to target both Gram-positive and Gram-negative bacteria while avoiding lysis of other cell types. However, the exact mechanism of how these peptides target, bind, and disrupt bacterial cell membranes is not understood. One specific peptide that has been shown to selectively capture bacteria is WLBU2 (sequence RRWVRRVRRWVRRVVRVVRRWVRR). It has been suggested that WLBU2 activity stems from the fact that when interacting with bacterial cell membranes the peptide assumes an α-helical structure and inserts itself into the membrane. To test this hypothesis, we applied sum frequency generation (SFG) spectroscopy and surface tensiometry to probe the peptide-lipid-air interface and identify the structure and monitor the interaction of WLBU2 with two model lipid monolayers that mimic mammalian and bacterial cell membranes. Model mammalian cell membranes were built upon zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipids while bacterial cell membranes were constructed with negatively charged 1,2-dimyristoyl-sn-glycero-3-phospho-(1’-rac-glycerol) (DMPG) lipids. The rate at which the surface pressure reaches equilibrium is 4.3 times faster for WLBU2 interacting with the negatively charged DMPG lipid monolayer than with the zwitterionic DPPC lipid monolayer. This observed WLBU2 binding affinity preference to negatively charged membranes is likely due to electrostatic interactions between positively charged amino acids within the peptide and negatively charged lipids. SFG studies at the peptide-lipid-air interface demonstrate that binding of WLBU2 induces increased lipid monolayer order. A larger increase in acyl chain order from 2.2 to 3.4 determined by the ratio of the CD3 symmetric (2075 cm-1) and CD2 symmetric (2100 cm-1) peak amplitudes suggest that WLBU2 is found at the surface of the zwitterionic phospholipid monolayer and not inserted. The amide I region SFG spectrum of WLBU2 interacting with the zwitterionic lipid monolayer shows two peaks near 1642 cm-1 and 1678 cm-1 indicative of an inactive β-sheet structure. A peak near 1651 cm-1 for WLBU2 interacting with negatively charged lipids is assigned to an active α-helix structure. Altogether, we demonstrate that WLBU2 shows a higher binding affinity to bacterial cell membranes and is in an active α-helix structure, alternatively in the presence of mammalian cell membranes in an inert β-sheet structure.