X-ray scattering with momentum transfer in the plane of membrane: Application to gramicidin organization
Huang, Huey W.
Master of Arts thesis
We demonstrate a technique of measuring x-ray (or neutron) scattering with the momentum transfer parallel to the plane of membrane. This technique allows us to investigate the lateral organization of protein and peptide in the membrane. To resolve the question of whether gramicidin (GA) forms lateral aggregates, samples of GA in dilauroylphosphatidycholine (DLPC) bilayers (molar ratio 1:10) were investigated. Very clear scattering signals of GA were obtained, even for the peptide without a heavy atom attached. The experiment showed that the gramicidin channels did not aggregate and were randomly distributed in the membrane. The non-conducting state of gramicidin channel was also investigated. We use a synthetic GA analogue in which the formyl group of natural GA is replaced by a BOC group. The in-plane scattering measurements show that the gramicidin channel closes by dissociation into two monomers, each remains embedded and freely diffuses in its own monolayer.