title: Closed state of gramicidin channel detected by X-ray in-plane scattering.
abstract: 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.
authors.affiliation: Physics Department, Rice University, Houston, TX 77251.
authors.forename: K
authors.initials: K
authors.lastname: He
authors.forename: S J
authors.initials: SJ
authors.lastname: Ludtke
authors.forename: Y
authors.initials: Y
authors.lastname: Wu
authors.forename: H W
authors.initials: HW
authors.lastname: Huang
authors.forename: O S
authors.initials: OS
authors.lastname: Andersen
authors.forename: D
authors.initials: D
authors.lastname: Greathouse
authors.forename: R E
authors.initials: RE
authors.lastname: Koeppe
mesh_terms: 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
chemical_list: D005563:Formic Acid Esters; D007473:Ion Channels; D008051:Lipid Bilayers; C000345:t-butyloxycarbonyl group; D006096:Gramicidin