Two-dimensional crystallization of the chaperonin TF55 from the hyperthermophilic archaeon Sulfolobus solfataricus

Oligomers of the chaperonin TF55 from Sulfolobus solfataricus have been successfully crystallized in two dimensions via their interaction with a phospholipid monolayer at the air/liquid interface. Oligomer orientation was dependent upon the lipid headgroup used. A neutral lipid monolayer gave rise to small paracrystalline areas of TF55 side views, whereas a negatively charged lipid monolayer resulted in large coherent crystalline areas of the chaperonin in an end-on orientation. These 2D crystals had p312 symmetry (a = b = 162 A, gamma = 60 degrees). Two-dimensional projection structures of the end-on arrays were produced by electron microscopy and image processing techniques. Under the conditions used to grow the crystals, the protein formed complexes of two stacked nine-subunit rings with threefold symmetry.