Abstract: Provided herein are multifunctional heteromultimer proteins. In specific embodiments is a heteromultimer comprising: at least two polypeptide constructs, each polypeptide construct comprising at least one cargo polypeptide attached to a transporter polypeptide, said transporter polypeptides derived from a monomeric native protein such that said monomeric constructs associate to form the heteromultimer and said transporter polypeptides associate to form a quasi-native structure of the monomeric native protein or analog thereof. These therapeutically novel molecules encompass heteromultimers comprising constructs that function as scaffolds for the conjugation or fusion of therapeutic molecular entities (cargo polypeptides) resulting in the creation of bispecific or multivalent molecular species. Provided herein is a method for creation of bispecific or multivalent molecular species.

Abstract: Provided herein are isolated heteromultimers comprising: at least one single domain antigen-binding construct attached to at least one monomer of a heterodimer Fc region; wherein the heterodimer Fc region comprises a variant CH3 domain comprising amino acid mutations that promote the formation of said heterodimer with stability comparable to that of a native Fc homodimer; and wherein said isolated heteromultimer is devoid of immunoglobulin light chains and optionally devoid of immunoglobulin CH1 region. These novel molecules comprise complexes of heterogeneous components designed to alter the natural way antibodies behave and that find use in therapeutics.

Abstract: The provided scaffolds have heavy chains that are asymmetric in the various domains (e.g. CH2 and CH3) to accomplish selectivity between the various Fc receptors involved in modulating effector function, beyond those achievable with a natural homodimeric (symmetric) Fc molecule, and increased stability and purity of the resulting variant Fc heterodimers. These novel molecules comprise complexes of heterogeneous components designed to alter the natural way antibodies behave and that find use in therapeutics.