X-RAY-SCATTERING IN THE PLANE OF MEMBRANE

We demonstrate a technique for measuring x-ray (or neutron) scattering with the momentum transfer oriented in the plane of a membrane, for the purpose of studying the lateral organization of proteins and peptides. As an example, the controversial question of whether gramicidin forms aggregates in membrane was investigated. We measured dilauroylphosphatidylcholine (DLPC) bilayers containing gramicidin in the molar ratio of 10:1. Very clear scattering curves reflecting gramicidin channel-channel correlation were obtained. Analysis of the data shows that the channels were randomly distributed in the membrane. We suggest that oriented proteins may provide substantial x-ray contrast against the lipid background without requiring heavy-atom labeling. This should open up many possible new experiments.