Synthesis, characterization, and black lipid membrane studies of [7-L-alanine] gramicidin A.
With a view to study the relevance of side-chain orientation in the transport of cations through a gramicidin transmembrane channel and to identify an analogue with favorable characteristics, [L-Ala7] gramicidin A was synthesized, purified, verified, and characterized by high-performance liquid chromatography, by carbon-13 and proton magnetic resonance spectra, and by circular dichroism spectra in methanol. Complete incorporation as the channel state was achieved when packaged in lysolecithin-containing lipid bilayers. The single-channel conductance data in diphytanoyllecithin/n-decane membranes are presented along with those of synthetic gramicidin A (GA). [L-Ala7] GA exhibits the highest most probable single-channel conductance so far reported for an analogue occurring at 28 pS as compared to 21 pS for GA under similar conditions. Also, a dramatic reduction in the dispersity of conducting states is observed with about 76% of the events falling in a narrow 1.75-pS conductance window as compared to about 31% of the events for GA under identical conditions. Thus, with the above characteristics, [L-Ala7]GA appears to be a very good candidate for a thorough study of ionic mechanism. The present results indicate that elements intrinsic to the channel proper are rate-limiting for GA and that there is no interfacial polarization or diffusion-controlled association at 1 M KCl and a 100-mV applied potential.
Prasad
K U
KU
Alonso-Romanowski
S
S
Venkatachalam
C M
CM
Trapane
T L
TL
Urry
D W
DW
D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D006096:Gramicidin / Q000138:chemical synthesis* / Q000031:analogs & derivatives; D007473:Ion Channels / Q000502:physiology; D009682:Magnetic Resonance Spectroscopy; D008567:Membranes, Artificial; D008958:Models, Molecular; D011487:Protein Conformation; D013329:Structure-Activity Relationship
D007473:Ion Channels; D008567:Membranes, Artificial; D006096:Gramicidin; C048452:gramicidin A, 7-alanine-