Structural and DNA-binding studies on the bovine antimicrobial peptide, indolicidin: evidence for multiple conformations involved in binding to membranes and DNA.
Indolicidin, a l3-residue antimicrobial peptide-amide, which is unusually rich in tryptophan and proline, is isolated from the cytoplasmic granules of bovine neutrophils. In this study, the structures of indolicidin in 50% D3-trifluoroethanol and in the absence and presence of SDS and D38-dodecylphosphocholine were determined using NMR spectroscopy. Multiple conformations were found and were shown to be due to different combinations of contact between the two WPW motifs. Although indolicidin is bactericidal and able to permeabilize bacterial membranes, it does not lead to cell wall lysis, showing that there is more than one mechanism of antimicrobial action. The structure of indolicidin in aqueous solution was a globular and amphipathic conformation, differing from the wedge shape adopted in lipid micelles, and these two structures were predicted to have different functions. Indolicidin, which is known to inhibit DNA synthesis and induce filamentation of bacteria, was shown to bind DNA in gel retardation and fluorescence quenching experiments. Further investigations using surface plasmon resonance confirmed the DNA-binding ability and showed the sequence preference of indolicidin. Based on our biophysical studies and previous results, we present a diagram illustrating the DNA-binding mechanism of the antimicrobial action of indolicidin and explaining the roles of the peptide when interacting with lipid bilayers at different concentrations.
Hsu
Chun-Hua
CH
Institute of Biological Chemistry, Academia Sinica Taipei, Taiwan.
Chen
Chinpan
C
Jou
Maou-Lin
ML
Lee
Alan Yueh-Luen
AY
Lin
Yu-Ching
YC
Yu
Yi-Ping
YP
Huang
Wei-Ting
WT
Wu
Shih-Hsiung
SH
D020816:Amino Acid Motifs; D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000378:metabolism; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D002417:Cattle; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D024202:Electrophoretic Mobility Shift Assay; D008051:Lipid Bilayers / Q000737:chemistry*; D008823:Micelles; D019906:Nuclear Magnetic Resonance, Biomolecular; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000737:chemistry; D011487:Protein Conformation; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D014270:Trifluoroethanol / Q000737:chemistry; D014867:Water / Q000737:chemistry
D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D008051:Lipid Bilayers; D008823:Micelles; D014867:Water; C073143:indolicidin; D010767:Phosphorylcholine; D012967:Sodium Dodecyl Sulfate; C028810:dodecylphosphocholine; D014270:Trifluoroethanol; D004247:DNA