EFFECT OF TRANSPLANTATION OF ANTIBODY HEAVY-CHAIN COMPLEMENTARITY-DETERMINING REGIONS ON LIGAND-BINDING

Active site structure-function analyses of anti-fluorescein single cha in antibody 4-4-20 and anti-single-stranded DNA single chain antibody 04-01 were conducted studying the ligand binding properties of hybrid antibodies resulting from systematic transplantation of heavy chain co mplementarity regions (HCDRs) from monoclonal antibody 4-4-20 into 04- 01. Two prototype monoclonal antibodies were chosen because the primar y structures of their respective light chains were nearly identical bu t the specificities and shape of their active sites were distinctly di fferent. Based on nearly identical light chains, the diverse active si te conformations (i.e. 4-4-20 pocket and 04-01 cleft) and subsequent s pecificities of the two antibodies were likely dictated by heavy chain properties, As a result, specificities of each HCDR transplant were a nalyzed in terms of binding reactivity with either fluorescein or (dT) (8). Results of binding studies, together with idiotypic and secondary structure analyses, were used to determine the relative contribution of each HCDR to the active site conformations and ligand specificities of monoclonal antibodies 4-4-20 and 04-01. Collectively the various a nalyses led to the conclusion that the intradomain conformational dyna mics and cooperativity necessary for the structural integrity of the l ow affinity cleft-shaped 04-01 anti-single-stranded DNA active site ar e probably less stringent than those of a high affinity pocket-shaped anti-fluorescein active site.