We study two-dimensional (2D) crystallization of streptavidin under low ionic strength conditions. We investigate crystals on both giant unilamellar lipid bilayer vesicles and lipid monolayers at the air-water interface. In contrast to 2D crystallization in high ionic strength buffers, the electrostatic repulsions under these conditions favor the low density C222 crystal form. The crystals grown on giant vesicles and those on lipid monolayers show the same crystal structure and similar crystallization trends despite the difference in surface geometries. When the ionic strength of the crystallization solution is progressively increased at pH 4, we observe a transition from C222 to the denser P1 space group commonly seen in high ionic strength conditions at this pH. A new crystal structure appears at intermediate ionic strength, illustrating the role of electrostatic repulsions in these ordering processes.