Ordering a Dynamic Protein Via a Small-Molecule Stabilizer

Like
many coactivators, the GACKIX domain of the master coactivator
CBP/p300 recognizes transcriptional activators of diverse sequence
composition via dynamic binding surfaces. The conformational dynamics
of GACKIX that underlie its function also render it especially challenging
for structural characterization. We have found that the ligand discovery
strategy of Tethering is an effective method for identifying small-molecule
fragments that stabilize the GACKIX domain, enabling for the first
time the crystallographic characterization of this important motif.
The 2.0 Å resolution structure of GACKIX complexed to a small
molecule was further analyzed by molecular dynamics simulations, which
revealed the importance of specific side-chain motions that remodel
the activator binding site in order to accommodate binding partners
of distinct sequence and size. More broadly, these results suggest
that Tethering can be a powerful strategy for identifying small-molecule
stabilizers of conformationally malleable proteins, thus facilitating
their structural characterization and accelerating the discovery of
small-molecule modulators.