Trehalose embedding technique for high-resolution electron crystallography: application to structural study on bacteriorhoposin

Trehalose was compared with glucose in its use as an embedding medium for the preparation of two-dimensional crystals for electron crystallographic structure analysis. Purple membranes (two-dimensional crystals of bacteriorhodopsin) embedded in either sugar were studied in a ‘partially hydrated’ as well as after ‘drying’ of the specimen. Diffraction patterns of the four conditions, all showing spots to a resolution better than 3.0 å, were analysed and merged. In the case of glucose embedded specimens, the merging Rfactor obtained from the diffraction patterns of dried specimens was significantly better than the one obtained from partially hydrated specimens. In the case of trehalose embedding, the merging R-factor for partially hydrated specimens was significantly better than the dried one. The trehalose embedded, partially hydrated specimens gave the best merging R-factor in all four cases.