Crystallization of Membrane Protein Nanoparticles

The self-assembly of membrane proteins from solution into two-dimensional crystals is studied numerically using a continuum model proposed by Talanquer and Oxtoby (J. Chem. Phys. 109, 223 (1998)). Although the mean field theory presented here is only qualitatively accurate in two dimensions, we obtain the main features of the crystal nucleation process, such as the nucleation free energy barrier and the number of particles and crystalline particles, respectively, in the critical nucleating droplet. Particular emphasis is given to the region near the metastable fluid-fluid coexistence curve, where the free energy barrier is small. The free energy barrier that separates a protein rich metastable fluid phase from its stable crystalline phase is studied for a variety of nucleation pathways in the metastable region. As in the three dimensional case of globular proteins, the nucleation barrier is smallest in the vicinity of the fluid-fluid critical point.