An Antibody with a Variable-Region Coiled-Coil "Knob" Domain

The X-ray crystal structure of a bovine antibody (BLV1H12) revealed a unique structure in its ultralong heavy chain complementarity determining region3 (CDR3H) that folds into a solvent-exposed -strand stalk fused to a disulfide crosslinked knob domain. We have substituted an antiparallel heterodimeric coiled-coil motif for the -strand stalk in this antibody. The resulting antibody (Ab-coil) expresses in mammalian cells and has a stability similar to that of the parent bovine antibody. MS analysis of H-D exchange supports the coiled-coil structure of the substituted peptides. Substitution of the knob-domain of Ab-coil with bovine granulocyte colony-stimulating factor (bGCSF) results in a stably expressed chimeric antibody, which proliferates mouse NFS-60 cells with a potency comparable to that of bGCSF. This work demonstrates the utility of this novel coiled-coil CDR3 motif as a means for generating stable, potent antibody fusion proteins with useful pharmacological properties.