ELECTRON CRYSTALLOGRAPHIC ANALYSIS OF 2-DIMENSIONAL STREPTAVIDIN CRYSTALS COORDINATED TO METAL-CHELATED LIPID MONOLAYERS

Coordination of individual histidine residues located on a protein sur face to metal-chelated lipid monolayers is a potentially general metho d for crystallizing proteins in two dimensions. It was shown recently by Brewster angle microscopy (BAM) that the model protein streptavidin binds via its surface histidines to Cu-DOIDA lipid monolayers, and ag gregates into regularly shaped domains that have the appearance of cry stals. We have used electron microscopy to confirm that the domains ar e indeed crystalline with lattice parameters similar to those of the s ame protein crystallized beneath biotinylated lipid monolayers, Althou gh BAM demonstrates that the two-dimensional protein crystals grown vi a metal chelation are distinct from the biotin-bound crystals in both microscopic shape and thermodynamic behavior, the two crystal types sh ow similar density projections and the same plane group symmetry.