Two-dimensional crystals of proteins on lipid layers

Proteins bound to lipid layers form single-layer (two-dimensional) crystals amenable to structure determination by electron microscopy and image processing. Recent studies have extended the range of the lipid-layer crystallization approach. In some cases, a simple electrostatic interaction between a protein and a charged lipid will suffice to direct binding, obviating the requirement for a specific lipid-binding ligand for two-dimensional crystal growth. Alternatively, streptavidin can be used to couple a biotinylated protein to a biotinylated lipid layer. Streptavidin itself forms large two-dimensional crystals that diffract to 2.8 A resolution, showing that ordering on lipid layers can be comparable to that in three dimensions.