Closed state of gramicidin channel detected by X-ray in-plane scattering.
An analogue of gramicidin A (gA) was synthesized with the formyl group replaced by a BOC group. The analogue (BOC-gA) exhibited single channel conduction, but the channel is 5-order-of-magnitude destabilized relative to the gA channel. Hydrated mixtures of gramicidin and dilauroyl phosphatidylcholine in the molar ratio of 1:10 were prepared into uniformly aligned multiple bilayers, and X-ray scattering with the momentum transfer in the plane of the membrane was measured. Analysis with the help of computer simulations showed that 70% of BOC-gA are monomers. Thus for the first time it was shown that gramicidin monomers are stable inside the monolayers of a lipid membrane. Furthermore, the monomers have the same beta helical conformation as the dimeric channel. The result suggests the possibility that when a gramicidin channel is closed, it dissociates into two monomers floating in opposite monolayers.
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Physics Department, Rice University, Houston, TX 77251.
Ludtke
S J
SJ
Wu
Y
Y
Huang
H W
HW
Andersen
O S
OS
Greathouse
D
D
Koeppe
R E
RE
D003198:Computer Simulation; D005563:Formic Acid Esters / Q000737:chemistry; D006096:Gramicidin / Q000737:chemistry*; D007473:Ion Channels / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry; D008954:Models, Biological; D012542:Scattering, Radiation; D014961:X-Ray Diffraction; D014965:X-Rays
D005563:Formic Acid Esters; D007473:Ion Channels; D008051:Lipid Bilayers; C000345:t-butyloxycarbonyl group; D006096:Gramicidin