Abstract: The present invention provides a method for preparing a modular scaffold that can bind to a target antigen and a method for engineering a bispecific functional agent consisting of an existing polypeptide binder fused at its C-terminus with said modular scaffold.

Abstract: The present invention provides a triple-mode antibody display system that simultaneously matures, displays and secretes an antibody to a target of interest. An antibody in vivo-matured and complexed with membrane anchored bait can be expressed on the surface of the host cell, while complexed with a soluble bait the antibody is secreted from the host cell. Methods of using the system for identifying binders that bind specifically to an antigen of interest are also provided. Polypeptides, polynucleotides and host cells useful for making the protein binder display system are also provided along with methods of use thereof.