Synthetic Models for Transmembrane Channels: Structural Variations That Alter Cation Flux
摘要:
Twelve novel bis- or tris(macrocyclic) compounds have been designed as models for cation-conducting channels that function in phospholipid bilayer vesicle membranes. In general, the channel model systems have the structure ''sidearm-crown-spacer-crown-spacer-crown-sidearm'', although certain features have been altered from compound to compound to assess the structure-activity relationship. Two additional compounds have been prepared exclusively as controls. The ionophores have been incorporated into the membranes either by warming the compound with the preformed vesicle or by incorporation during vesicle formation. The two methods gave identical results within experimental error. Cation flux was assessed by two different analytical methods. In one case, the fluorescent dye pyranine was encapsulated within vesicles containing ionophore. Proton transport was then monitored by changes in dye fluorescence with time following an acid pulse. Ionophoretic activity far most of the compounds was studied using a dynamic NMR method in which the flux rate of Na-23(+) through the bilayer was monitored. All NMR studies were done in conjunction with gramicidin as a control to minimize experimental variations from run to run. Several of the synthetic ionophores showed cation conduction of as much as 40% of the activity of gramicidin. Apparently, small structural changes significantly altered flux rates and two known carriers closely related to the channel formers failed to exhibit measurable transport under comparable conditions.
The influence of varied amide bond positions on hydraphile ion channel activity
作者:Michelle E. Weber、Wei Wang、Sarah E. Steinhardt、Michael R. Gokel、W. Matthew Leevy、George W. Gokel
DOI:10.1039/b510863m
日期:——
Hydraphile compounds have been prepared in which certain of the amine nitrogens have been replaced by amide residues. The amide bonds are present either in the sidearm, the side chain, or the central relay. Sodiumcationtransport through phospholipid vesicles mediated by each hydraphile was assessed. All of the amide-containing hydraphiles showed increased levels of Na(+) transport compared to the
Activity of synthetic ion channels is influenced by cation–π interactions with phospholipid headgroups
作者:Michelle E. Weber、Elizabeth K. Elliott、George W. Gokel
DOI:10.1039/b513179k
日期:——
A suite of synthetichydraphile ion channels has been used to probe the possibility of cation-pi interactions between the channel and the phospholipid bilayer. The hydraphiles selected for this study contained either no sidearm, aliphatic sidearms or aromatic sidearms that varied in electron-richness. An ion selective electrode (ISE) method was used to evaluate the ion transport ability of these hydraphiles
Planar Bilayer Conductance and Fluorescence Studies Confirm the Function and Location of a Synthetic, Sodium-Ion-Conducting Channel in a Phospholipid Bilayer Membrane
作者:Ernesto Abel、Glenn E. M. Maguire、Eric S. Meadows、Oscar Murillo、Takashi Jin、George W. Gokel
DOI:10.1021/ja971098t
日期:1997.9.1
Hydraphile Channels: Structural and Fluorescent Probes of Position and Function in a Phospholipid Bilayer
作者:Ernesto Abel、Glenn E. M. Maguire、Oscar Murillo、Iwao Suzuki、Stephen L. De Wall、George W. Gokel
DOI:10.1021/ja9909172
日期:1999.10.1
Three novel tris(macrocycle)s having fluorescent residues at their distal termini have been prepared and studied. The compounds are of the form R[N18N]C-12[N18N]C-12[N18N]R in which R is 2-(3-indolyl)ethyl (1), 2-(3-(N-methylindolyl))ethyl (2), and dansyl (3). Compounds 2 and 3 were found to transport Naf at rates similar to those of other tris(macrocyclic)s but 1 was not an ionophore in the bilayer as assessed by Na-23 NMR analysis. The latter failure may be due to a hydrogen-bond blockade leading to a globular conformation adopted by the hydraphile. The fluorescence maximum of 3 was determined in a variety of solvents and in a phospholipid bilayer. The polarity experienced by the dansyl group in the bilayer was intermediate between that observed in methanol and ethanol. Fluorescence depth quenching using doxyl-substituted lipids showed that the dansyl headgroups of 3 were 14 Angstrom from the bilayer's midplane or separated by about 28 Angstrom. Fluorescence energy transfer between 2 acid 3 showed that these two hydraphiles were not appreciably aggregated in the bilayer.
The presence of cholestanyl substituents in hydraphile channels inhibits cation transport in the phospholipid bilayer
作者:Eric S Meadows、Ernesto Abel-Santos、Daniel C Frankel、George W Gokel
DOI:10.1016/s0040-4039(00)00068-x
日期:2000.3
The presence of steroids within a synthetic, cation channel model compound restricts or prevents the passage of Na+ through the phospholipid bilayer owing to collapse of the pore induced by hydraphobic contacts (C) 2000 Elsevier Science Ltd. All rights reserved.