Binding proteins antigens, tetravalent and bispecific

A binding protein tetravalent bispecific antigen, comprising: a) a modified first antibody which specifically binds to a first antigen, and on whose C-terminus of said heavy chain fused so heavy chain additional VH-CH1 domains of the first antibody by their N-terminal; b) two light chains of said first antibody a); c) a modified second antibody which binds specifically to a second antigen heavy chain in which the CH1 domain is on whose C-terminus of said heavy chain replaced with the domain CL of said second antibody and additionally fuse the VH-CL domains of said second antibody through its N-terminal; d) two light chains of said second modified antibody c), in which the domain CL is replaced by the CH1 domain of said second antibody.