Low-resolution structures of OmpA⋅DDM protein-detergent complexes.

We have used SAXS to determine the low-resolution structure of the outer-membrane protein OmpA from E. coli solubilized by the surfactant dodecyl maltoside (DDM). We have studied three variants of the transmembrane domain of OmpA-namely monomers, self-associated dimers, and covalently linked dimers-as well as the monomeric species of the full-length protein with the periplasmic domain. We can successfully model the structures of the monomeric and covalently linked dimer as one and two natively folded proteins in a DDM micelle, respectively, whereas the noncovalently linked dimer presents a more complicated structure, possibly due to higher-order species. We have determined the structure of the full-length protein to be that of a globular periplasmic domain attached through a flexible linker to the transmembrane domain. This approach provides valuable information about how membrane proteins are embedded in amphiphilic environments.