Abstract: The present invention provides polypeptides comprising modified human, humanized, or chimeric immunoglobulin heavy chain variable domains. Corresponding antibodies, variants, fragments, nucleic acids, vectors, phages, libraries, methods and kits are also provided.

Abstract: The current invention relates to means and methods for producing and isolating immunoglobulin proteins comprising a first and a second immunoglobulin polypeptide, in particular to means and methods for producing, and separating proteins comprising said first and second immunoglobulin polypeptide. By including variations to amino acids, and variant separation domains from a cell producing the desired immunoglobulin protein, a desired immunoglobulin protein as produced can be separated from mixtures of immunoglobulin proteins.