W0433

Two Dimensional Protein Crystals on Lipid Layers: Structure, Morphology and Mechanical Properties. Alice P. Gast^Ψ, Pasut Ratanabanangkoon^§, Michael Gropper^†, Rudolf Merkel^‡ and Erich Sackmann^†, ^ΨDept. of Chemical Engineering, Massachusetts Inst. of Technology, Cambridge, MA, 02139, ^§Transform Pharma, Lexington, MA 02421, ^†Dept. of Biophysics – E22, Technical Univ. of Munich, D-85748 Garching, Germany, ^‡Forschungszentrum Jülich, Inst. für Schichten und Grenzflächen (ISG-4), D-52425 Jülich, Germany.

The ordering of proteins in two-dimensions (2D) is of interest as a fundamental model of phase transitions and self-assembly. It is also a phenomenon found in nature on the surface of some bacteria and phages. In some cases the structure and organization of the protein coating imparts structural and mechanical integrity to the cell. The ability to create and manipulate protein monolayers on vesicles requires understanding and control of the various intermolecular forces involved.

We are studying the macroscopic morphology and molecular arrangement of two-dimensional streptavidin crystals bound to biotinylated lipid monolayers at the air-water interface and in bilayer vesicles. We show how the symmetry breaking in the binding process alters crystal morphology and how changing the pH and ionic strength of the sub-phase can change the crystalline lattice structure. Then, using our understanding of the key interactions between neighboring proteins, we make point mutations to alter these interactions and change the crystal structure. Finally mixing wild-type and mutant proteins we can further tailor the crystal structure and morphology. Producing these crystals on the surface of vesicles provides analogies with protein coats on cell surfaces. We will discuss the influence of an ordered layer of proteins on the mechanical properties of lipid vesicles.