Computational Design of an Allosteric Antibody Switch by Deletion and Rescue of a Complex Structural Constellation
2020
Therapeutic
monoclonal antibodies have transformed medicine, especially
with regards to treating cancers and disorders of the immune system.
More than 50 antibody-derived drugs have already reached the clinic,
the majority of which target cytokines or cell-surface receptors.
Unfortunately, many of these targets have pleiotropic functions: they
serve multiple different roles, and often not all of these roles are
disease-related. This can be problematic because antibodies act throughout
the body, and systemic neutralization of such targets can lead to
safety concerns. To address this, we have developed a strategy whereby
an antibody’s ability to recognize its antigen is modulated
by a second layer of control, relying on addition of an exogenous
small molecule. In previous studies, we began to explore this idea
by introducing a deactivating tryptophan-to-glycine mutation in the
domain–domain interface of a single-chain variable fragment
(scFv), and then restoring activity by adding back indole to fit the
designed cavity. Here, we now describe a novel computational strategy
for enumerating larger cavities that can be formed by simultaneously
introducing multiple adjacent large-to-small mutations; we then carry
out a complementary virtual screen to identify druglike compounds
to match each candidate cavity. We first demonstrate the utility of
this strategy in a fluorescein-binding single-chain variable fragment
(scFv) and experimentally characterize a triple mutant with reduced
antigen-binding (Rip-3) that can be rescued using a complementary
ligand (Stitch-3). Because our design is built upon conserved residues
in the antibody framework, we then show that the same mutation/ligand
pair can also be used to modulate antigen-binding in an scFv build
from a completely unrelated framework. This set of residues is present
in many therapeutic antibodies as well, suggesting that this mutation/ligand
pair may serve as a general starting point for introducing ligand-dependence
into many clinically relevant antibodies.
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