Structural Basis of TLR2/TLR1 Activation by the Synthetic Agonist Diprovocim

Diprovocim is a recently discovered
exceptionally potent, synthetic
small molecule agonist of TLR2/TLR1 and has shown significant adjuvant
activity in anticancer vaccination against murine melanoma. Since
Diprovocim bears no structural similarity to the canonical lipopeptide
ligands of TLR2/TLR1, we investigated how Diprovocim interacts with
TLR2/TLR1 through in vitro biophysical, structural, and computational
approaches. We found that Diprovocim induced the formation of TLR2/TLR1
heterodimers as well as TLR2 homodimers in vitro. We determined the
crystal structure of Diprovocim in a complex with a TLR2 ectodomain,
which revealed, unexpectedly, two Diprovocim molecules bound to the
ligand binding pocket formed between two TLR2 ectodomains. Extensive
hydrophobic interactions and a hydrogen-bonding network between the
protein and Diprovocim molecules are observed within the defined ligand
binding pocket and likely underlie the high potency of Diprovocim.
Our work shed first light into the activation mechanism of TLR2/TLR1
by a noncanonical agonist. The structural information obtained here
may be exploited to manipulate TLR2/TLR1-dependent signaling.