TWO-DIMENSIONAL CRYSTALLISATION MEMBRANE PROTEINS. Werner Kühlbrandt, European Molecular Biology Laboratory, Meyerhofstr. 1, 69117 Heidelberg, Germany.

Two-dimensional (2D) crystals are used increasingly successfully for determining the structure of membrane proteins at high and medium resolution of electron cryo-microscopy. Membrane proteins are often not available in quantities sufficient for 3D crystallisation trials, and not many have yielded highly ordered 3D crystals for X-ray crystallography. 2D crystallisation of membrane proteins requires less material and tends to occur more readily than 3D crystallisation, due to the special nature of these proteins which favours in-plane hydrophobic interactions.

Different mechanisms of 2D crystal formation will be discussed, and recent examples will be presented. The structure of the plant light-harvesting complex (LHC-II) which was determined by electron crystallography of 2D crystals at 3.4 Å resolution will be described briefly.