Immune complex formation, which structure of a protein is involved?

The primary structure is the sequence of the amino acids in a polypeptide chain.Secondary structure is the folding of sho (3- to 30-residue), contiguous segments of the polypeptide into geometrically ordered units.Teiary structure is the assembly of secondary structural units into larger functional units such as the mature polypeptide and its component domains.The specific biological function of each immunoglobulin class is determined by the teiary structure of the constant domains (Fc region).