Study of allosteric communication between protomers by immunotagging.

Ligand-induced allosteric changes in proteins are important in their cellular functions and regulation, and both concerted and sequential examples are known. The distinction has entailed elaborate analysis, however, and only a few systems have been unequivocally analysed. We have investigated the coupling between ATP usage and DNA transport by type II DNA topoisomerases, and one key question concerning allostery in these dyadic enzymes is whether ATP binding to one protomer can induce a concerted conformational change in the entire enzyme. Here we use an enzyme with one immunotagged subunit defective in ATP binding and one wild-type subunit to show that it can. Our approach should be generally applicable in the study of allostery and communication between members of a macromolecular assembly.