Provided herein are binding proteins comprising one or more
immunoglobulin Fc region hinge, CH2, and / or CH3 domain wherein one or more hinge and / or
constant region CH2 and / or CH3 domain is modified to alter the
binding protein's binding affinity and / or specificity for a cognate
receptor (e.g., an
Fc receptor) and / or to impart one or more new binding specificity(ies) to the hinge and / or
constant region that the corresponding unmodified immunoglobulin does not possess (e.g., affinity for distinct class of cognate
receptor distinct from the class of cognate
receptor to which the unmodified
binding protein specifically binds). Binding proteins according to the present invention include, for example, modified antibodies,
antibody fragments, recombinant binding proteins, and molecularly engineered
binding domain-immunoglobulin fusion proteins, including small modular immunopharmaceutical products (SMIP™ products).