Structure-function characterization and optimization of a plant-derived antibacterial peptide.
Crushed seeds of the Moringa oleifera tree have been used traditionally as natural flocculants to clarify drinking water. We previously showed that one of the seed peptides mediates both the sedimentation of suspended particles such as bacterial cells and a direct bactericidal activity, raising the possibility that the two activities might be related. In this study, the conformational modeling of the peptide was coupled to a functional analysis of synthetic derivatives. This indicated that partly overlapping structural determinants mediate the sedimentation and antibacterial activities. Sedimentation requires a positively charged, glutamine-rich portion of the peptide that aggregates bacterial cells. The bactericidal activity was localized to a sequence prone to form a helix-loop-helix structural motif. Amino acid substitution showed that the bactericidal activity requires hydrophobic proline residues within the protruding loop. Vital dye staining indicated that treatment with peptides containing this motif results in bacterial membrane damage. Assembly of multiple copies of this structural motif into a branched peptide enhanced antibacterial activity, since low concentrations effectively kill bacteria such as Pseudomonas aeruginosa and Streptococcus pyogenes without displaying a toxic effect on human red blood cells. This study thus identifies a synthetic peptide with potent antibacterial activity against specific human pathogens. It also suggests partly distinct molecular mechanisms for each activity. Sedimentation may result from coupled flocculation and coagulation effects, while the bactericidal activity would require bacterial membrane destabilization by a hydrophobic loop.
Suarez
Mougli
M
Institute of Biotechnology, University of Lausanne, Switzerland.
Haenni
Marisa
M
Canarelli
Stéphane
S
Fisch
Florian
F
Chodanowski
Pierre
P
Servis
Catherine
C
Michielin
Olivier
O
Freitag
Ruth
R
Moreillon
Philippe
P
Mermod
Nicolas
N
D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects; D003470:Culture Media; D004926:Escherichia coli / Q000187:drug effects; D005658:Fungi / Q000187:drug effects; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D013058:Mass Spectrometry; D008826:Microbial Sensitivity Tests; D018613:Microscopy, Confocal; D008961:Models, Structural; D008969:Molecular Sequence Data; D029587:Moringa / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry* / Q000494:pharmacology*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012639:Seeds / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013329:Structure-Activity Relationship
D000900:Anti-Bacterial Agents; D003470:Culture Media; D010455:Peptides