Alamethicin pyromellitate: an ion-activated channel-forming peptide.
The synthesis and characterization of alamethicin pyromellitate (Alm-PM), a derivative of the channel-forming peptide alamethicin bearing three negative charges at the C-terminus, is described. The self-association of Alm-PM in small unilamellar vesicles of dioleoylphosphatidylcholine (DOPC), monitored using circular dichroism (CD) spectroscopy, occurs much less readily than the self-association of unmodified alamethicin. Channel formation by Alm-PM also occurs less readily and exhibits a higher voltage threshold for activation in planar lipid bilayers and in lipid vesicles. An increase in the salt concentration, and particularly the addition of calcium ions, promotes Alm-PM self-association as monitored by CD spectroscopy. Calcium also facilitates channel formation by Alm-PM both in planar lipid bilayers and in lipid vesicles by lowering the voltage threshold for activation. Thus Alm-PM behaves as an ion-activated ion channel. These results indicate that the self-association of alamethicin-like peptides in membranes is critical for channel formation and that transmembrane flip-flop of peptide helices is not required. In addition, these results demonstrate that the activity of channel-forming peptides may be controlled by controlling the process of self-association.
Woolley
G A
GA
Department of Chemistry, University of Toronto, Canada.
Epand
R M
RM
Kerr
I D
ID
Sansom
M S
MS
Wallace
B A
BA
D000408:Alamethicin / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D000595:Amino Acid Sequence; D002942:Circular Dichroism; D007473:Ion Channels / Q000737:chemistry*; D007477:Ions; D008051:Lipid Bilayers / Q000737:chemistry; D008956:Models, Chemical; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence
D007473:Ion Channels; D007477:Ions; D008051:Lipid Bilayers; C087605:alamethicin F50 pyromellitate; D000408:Alamethicin