  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.
