Biomolecules can act as functional templates for the organization of inorganic particles. Here we use two protein containers, engineered with opposite surface charge, as building blocks for the construction of a new type of biohybrid material. Binary structures with crystalline order were obtained, adopting a tetragonal lattice. Moreover, the cavity of the engineered protein containers can be filled with inorganic nanoparticles. The controlled assembly of these protein-nanoparticle composites yields highly ordered binary nanoparticle super lattices as free-standing, crystals, with up to a few hundred micrometers in size. Because the structure and lattice parameters of the protein-nanoparticle crystals are independent of their nanoparticle cargo, the binary protein material may serve as a generally applicable matrix for the assembly of a variety of nanoparticles types.