Voltage-dependent behavior of a "ball-and-chain" gramicidin channel.
The channel-forming properties of two analogs of gramicidin, gramicidin-ethylenediamine (gram-EDA), and gramicidin-N,N-dimethylethylenediamine (gram-DMEDA) were studied in planar lipid bilayers, using protons as the permeant ion. These peptides have positively charged amino groups tethered to their C-terminal ends via a linker containing a carbamate group. Gram-DMEDA has two extra methyl groups attached to the terminal amino group, making it a bulkier derivative. The carbamate groups undergo thermal cis-trans isomerization on the 10-100-ms time scale. The conductance behavior of gram-EDA is found to be markedly voltage dependent, whereas the behavior of gram-DMEDA is not. In addition, voltage affects the cis-trans ratios of the carbamate groups of gram-EDA, but not those of gram-DMEDA. A model is proposed to account for these observations, in which voltage can promote the binding of the terminal amino group of gram-EDA to the pore in a "ball-and-chain" fashion. The bulkiness of the gram-DMEDA derivative prevents this binding.
Woolley
G A
GA
Department of Chemistry, University of Toronto, Ontario, Canada. awoolley@chem.utoronto.ca
Zunic
V
V
Karanicolas
J
J
Jaikaran
A S
AS
Starostin
A V
AV
D000595:Amino Acid Sequence; D002219:Carbamates / Q000737:chemistry / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology; D006096:Gramicidin / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry* / Q000378:metabolism; D007536:Isomerism; D008051:Lipid Bilayers / Q000378:metabolism; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011522:Protons
D002219:Carbamates; D002712:Chlorides; D007473:Ion Channels; D008051:Lipid Bilayers; D011522:Protons; D006096:Gramicidin