The Speed of Allosteric Signaling Within a Single-Domain Protein

While much is known about different allosteric regulation mechanisms, the nature of the "allosteric signal", and the timescale on which it propagates, remains elusive. The PDZ3 domain from postsynaptic density-95 protein is a small protein domain with a terminal third alpha helix -- the $\alpha$3-helix, which is known to be allosterically active. By cross-linking the allosteric helix with an azobenzene moiety, we obtained a photocontrollable PDZ3 variant. Photoswitching triggers its allosteric transition, resulting in a change in binding affnity of a peptide to the remote binding pocket. Using time-resolved infrared and UV/Vis spectroscopy, we follow the allosteric signal transduction and reconstruct the timeline in which the allosteric signal propagates through the protein within 200 ns.