Readily isolated bispecific antibodies with native immunoglobulin format

FIELD: chemistry. SUBSTANCE: invention relates to biochemistry. Described is a bispecific antigen-binding protein which is heterodimeric with respect to binding protein A. The protein contains a first polypeptide comprising, from N-terminal to C-terminal, a first epitope-binding region that selectively binds a first epitope, an immunoglobulin constant region that comprises a first CH3 region of a human IgG selected from IgG1, IgG2, and IgG4, where the first CH3 region binds with protein A, and a second polypeptide comprising, from N-terminal to C-terminal, a second epitope-binding region that selectively binds a second epitope, an immunoglobulin constant region that comprises a second CH3 region of a human IgG selected from IgG1, IgG2, and IgG4, where the second CH3 region comprises a modification that reduces or prevents binding of the second CH3 domain to protein A. EFFECT: invention enables rapid isolation of protein A. 9 cl, 10 dwg, 3 tbl, 12 ex