ELECTRON CRYSTALLOGRAPHY OF STREPTAVIDIN MONOLAYER CRYSTAL

Baylor College Of Medicine, Houston TX

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Abstract

Two-dimensional crystallization of soluble proteins on phospholipid monolayers continues to draw the interest of structural biologists and bio-material engineers. This type of 2D periodic array can be used for high resolution structural studies by electron crystallography, for seeding of three-dimensional crystal growth, as biosensors or as templates of new material synthesis. Coordination of individual histidine residues located on a protein to metal-chelated lipid monolayers is a potentially general method to crystallize proteins in two dimensions. It was shown recently by Brewster angle microscopy that the model protein streptavidin binds via its surface histidines to Cu-DOIDA-lipid monolayers, and aggregates into regularly shaped domains that have the appearance of crystals. We have used electron microscopy to confirm that the domains are indeed crystalline with lattice parameters similar to those of the protein crystallized underneath biotinylated monolayers. Although BAM demonstrates that the two-dimensional protein crystals grown via metal chelation are distinct from the biotin-bound crystals in both microscopic shape and thermodynamic behavior (i.e. different crystal habits), the two crystal types show similar electron density projections and the same plane group symmetry.