Screening of inhibitory Ab1
antibodies is a critical step for producing
catalytic antibodies in the anti-idiotypic approach. However, the incompatible surface of the active site of the
enzyme and the
antigen-binding site of heterotetrameric conventional
antibodies become the limiting step. Because camelid-derived
nanobodies possess the potential to preferentially bind to the active site of
enzymes due to their small size and long CDR3, we have developed a novel approach to produce
antibodies with
alliinase activities by exploiting the molecular mimicry of camel
nanobodies. By screening the camelid-derived variable region of the heavy chain
cDNA phage display library with
alliinase, we obtained an inhibitory nanobody VHHA4 that recognizes the active site. Further screening with VHHA4 from the same variable domain of the heavy chain of a heavy-chain antibody library led to a higher incidence of anti-idiotypic Ab2 abzymes with
alliinase activities. One of the abzymes, VHHC10, showed the highest activity that can be inhibited by Ab1 VHHA4 and
alliinase competitive inhibitor
penicillamine and significantly suppressed the B16
tumor cell growth in the presence of
alliin in vitro. The results highlight the feasibility of producing abzymes via anti-idiotypic nanobody approach.