Stably tethered structures of defined compositions with multiple functions or binding specificities

A stably tethered structure comprising:

• a) two copies of a first fusion protein comprising the amino acid sequence selected from DDD1 (SEQ ID NO:
• 1) and DDD2 (SEQ ID NO:
• 2) fused to a first protein or peptide;
• and
• b) one copy of a second fusion protein comprising the amino acid sequence selected from AD1 (SEQ ID NO:
• 3) and AD2 (SEQ ID NO:
• 4) fused to a second protein or peptide;
• wherein the two DDD sequences bind to the AD sequence to form a stably tethered structure and wherein the first and second proteins or peptides are selected from the group consisting of a cytokine, an antibody, a Fab antibody fragment, a Fab′ antibody fragment, an scFv antibody fragment, a diabody and a single domain antibody (DAB).

A stably tethered structure comprising:

• a) two copies of a first fusion protein comprising an amino acid sequence selected from DDD1 (SEQ ID NO:1) and DDD2 (SEQ ID NO:2) fused to a first protein or peptide;
• and
• b) one copy of a second fusion protein comprising an amino acid sequence selected from AD1 (SEQ ID NO:3) and AD2 (SEQ ID NO:4) fused to a second protein or peptide;
• wherein the two DDD sequences bind to the AD sequence to form a stably tethered structure and wherein the first and second protein or peptide is selected from the group consisting of an IgG antibody, a Fab antibody fragment, an scFv antibody fragment and a cytokine.