Bucki, Robert

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  • Publication
    Antibacterial Activities of Rhodamine B-Conjugated Gelsolin-Derived Peptides Compared to Those of the Antimicrobial Peptides Cathelicidin LL37, Magainin II, and Melittin
    (2004-05-01) Bucki, Robert; Pastore, Jennifer J; Randhawa, Paramjeet; Vegners, Rolands; Janmey, Paul; Wiener, Daniel J
    The growing number of antibiotic-resistant bacteria necessitates the search for new antimicrobial agents and the principles by which they work. We report that cell membrane-permeant rhodamine B (RhB)-conjugated peptides based on the phosphatidylinositol-4,5-bisphosphate binding site of gelsolin can kill the gram-negative organisms Escherichia coli and Pseudomonas aeruginosa and the gram-positive organism Streptococcus pneumoniae. RhB linkage to the QRLFQVKGRR sequence in gelsolin was essential for the antibacterial function, since the unconjugated peptide had no effect on the bacteria tested. Because RhB-QRLFQVKGRR (also termed PBP10), its scrambled sequence (RhB-FRVKLKQGQR), and PBP10 synthesized from D-isomer amino acids show similar antibacterial properties, the physical and chemical properties of these derivatives appear to be more important than specific peptide folding for their antibacterial functions. The similar activities of PBP10 and all-D-amino-acid PBP10 also indicate that a specific interaction between RhB derivatives and bacterial proteins is unlikely to be involved in the bacterial killing function of PBP10. By using a phospholipid monolayer system, we found a positive correlation between the antibacterial function of PBP10, as well as some naturally occurring antibacterial peptides, and the intrinsic surface pressure activity at the hydrophobic-hydrophilic interface. Surprisingly, we observed little or no dependence of the insertion of these peptides into lipid monolayers on the phospholipid composition. These studies show that an effective antimicrobial agent can be produced from a peptide sequence with specificity to a phospholipid not found in bacteria, and comparisons with other antimicrobial agents suggest that the surface activities of these peptides are more important than specific binding to bacterial proteins or lipids for their antimicrobial functions.
  • Publication
    Interaction of the Gelsolin-Derived Antibacterial PBP 10 Peptide with Lipid Bilayers and Cell Membranes
    (2006-09-01) Bucki, Robert; Janmey, Paul
    PBP 10, an antibacterial, cell membrane-permeant rhodamine B-conjugated peptide derived from the polyphosphoinositide binding site of gelsolin, interacts selectively with both lipopolysaccharides (LPS) and lipoteichoic acid (LTA), the distinct components of gram-negative and gram-positive bacteria, respectively. Isolated LPS and LTA decrease the antimicrobial activities of PBP 10, as well as other antimicrobial peptides, such as cathelicidin-LL37 (LL37) and mellitin. In an effort to elucidate the mechanism of bacterial killing by PBP 10, we compared its effects on artificial lipid bilayers and eukaryotic cell membranes with the actions of the mellitin, magainin II, and LL37 peptides. This study reveals that pore formation is unlikely to be involved in PBP 10-mediated membrane destabilization. We also investigated the effects of these peptides on platelets and red blood cells (RBCs). Comparison of these antimicrobial peptides shows that only mellitin has a toxic effect on platelets and RBCs in a concentration range concomitant with its bactericidal activity. The hemolytic activities of the PBP 10 and LL37 peptides significantly increase when RBCs are osmotically swollen in hypotonic solution, indicating that these antibacterial peptides may take advantage of the more extended form of bacterial membranes in exerting their killing activities. Additionally, we found that LL37 hemolytic activity was much higher when RBCs were induced to expose phosphatidylserine to the external leaflet of their plasma membranes. This finding suggests that asymmetrical distribution of phospholipids in the external membranes of eukaryotic cells may represent an important factor in determining the specificity of antibacterial peptides for targeting bacteria rather than eukaryotic cells.