W0241

Lessions from 2-D Protein Crystals: Protein-Protein Contacts, Growth Kinetics and Dissolution. Viola Vogel, Sandy Koppenol, William R. Schief, Todd Edwards, Wolfgang Frey, and Patrick Stayton, Department of Bioengineering, University of Washington, Seattle, WA 98195. USA

The two-dimensional crystallization of streptavidin underneath functionalized lipid monolayer systems provides an opportunity to map macroscopic crystallization properties such as morphology and crystal phase to molecular events such as protein-protein contacts and interfacial binding dynamics. The 2-D crystallization process of streptavidin has been analyzed by Brewster angle microscopy (BAM), where the grayscale of the BAM images provides a direct measure of the local protein surface density. This allows determination of the critical surface density required to initiate protein crystallization, and to probe the crystal growth kinetics and their morphology. We will discuss the role of critical residues within the protein-protein contacts and within the biotin binding site on the noncrystalline-to-crystalline phase transition of streptavidin, and how alterations of its affinity to surface tethered ligands impacts the critical surface density. For example, we found that the electrostatic interaction of the two opposing lysines 132 at the crystal contact interfaces is responsible for ionic strength dependence of streptavidin crystallization. It is also a key determinant of the kinetic barriers controlling crystal morphology.