Closed state of gramicidin channel detected by X-ray in-plane scattering

• Published in: Biophysical chemistry Vol. 49; no. 1; pp. 83 - 89
• Main Authors: He, K., Ludtke, S.J., Wu, Y., Huang, H.W., Andersen, O.S., Greathouse, D., Koeppe, R.E.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.02.1994
• Subjects: Computer Simulation; Formic Acid Esters - chemistry; Gramicidin; Gramicidin - chemistry; Ion Channels - chemistry; Lipid Bilayers - chemistry; Lipid membranes; Models, Biological; Monomers; Scattering, Radiation; X-Ray Diffraction; X-ray scattering; X-Rays; Lipid membranes; X-ray scattering; Gramicidin; Monomers
• ISSN: 0301-4622; 1873-4200
• DOI: 10.1016/0301-4622(93)E0085-J

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 β 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.