Structure characterization of membrane bound and surface adsorbed protein.

X-ray standing waves (XSW) have been used to study the topology of the protein cytochrome c, bound to a negatively charged model membrane and adsorbed at a metal surface. At the metal surface, cytochrome c forms an hexagonally close-packed monolayer. A similar packing arrangement is observed at the surface of a self-assembled lipid film on silver. The data suggest that cytochrome c maintains its native globular structure upon surface binding and subsequent storage for an extended period. Further, the data are consistent with a protein docking mechanism wherein the heme plane is oriented perpendicular to and with its exposed edge facing the surface. This study demonstrates the utility of XSW as a new and powerful structural tool for investigating membrane- and surface-protein interactions.