Design rules for the self-assembly of a protein crystal

Theories of protein crystallization based on spheres that form close-packed crystals predict optimal assembly within a ‘slot’ of second virial coefficients and enhanced assembly near the metastable liquid–vapor critical point. However, most protein crystals are open structures stabilized by anisotropic interactions. Here, we use theory and simulation to show that assembly of one such structure is not predicted by the second virial coefficient or enhanced by the critical point. Instead, good assembly requires that the thermodynamic driving force be on the order of the thermal energy and that interactions be made as nonspecific as possible without promoting liquid–vapor phase separation.