Molecular assembly and interfaces present in the crystal lattice. IgD1 and IgD2 are colored in cyan and wheat, respectively. The assemblies were dissected and shown separately. (A) A representative array of IgD1-D2 molecular packing in the crystal lattice. The 2 molecules of the strand-swapped dimer form 2 layers of lattice contacts marked with dashed lines. One layer of the contacts is shown by rotating the molecule 90° along the y-axis with the interfaces indicated by the arrows. (B) The assembly of a tetramer formed by 2 strand-swapped dimers crossed at the bridge region. (C) The assembly of a tetramer formed by IgD1/D1 interactions.