Satapathy, Ajit K.Richardson, Charles C.2019-10-052011Satapathy, Ajit K., and Charles C. Richardson. 2011. “The Glutamate Switch of Bacteriophage T7 DNA Helicase.” Journal of Biological Chemistry 286 (26): 23113–20. https://doi.org/10.1074/jbc.m111.218651.0021-92581083-351Xhttp://nrs.harvard.edu/urn-3:HUL.InstRepos:41483312The DNA helicase encoded by gene 4 of bacteriophage T7 forms a hexameric ring in the presence of dTTP, allowing it to bind DNA in its central core. The oligomerization also creates nucleotide-binding sites located at the interfaces of the subunits. DNA binding stimulates the hydrolysis of dTTP but the mechanism for this two-step control is not clear. We have identified a glutamate switch, analogous to the glutamate switch found in AAA + enzymes that couples dTTP hydrolysis to DNA binding. A crystal structure of T7 helicase shows that a glutamate residue (Glu-343), located at the subunit interface, is positioned to catalyze a nucleophilic attack on the gamma-phosphate of a bound nucleoside 5'-triphosphate. However, in the absence of a nucleotide, Glu-343 changes orientation, interacting with Arg-493 on the adjacent subunit. This interaction interrupts the interaction of Arg-493 with Asn-468 of the central beta-hairpin, which in turn disrupts DNA binding. When Glu-343 is replaced with glutamine the altered helicase, unlike the wild-type helicase, binds DNA in the presence of dTDP. When both Arg-493 and Asn-468 are replaced with alanine, dTTP hydrolysis is no longer stimulated in the presence of DNA. Taken together, these results suggest that the orientation of Glu-343 plays a key role in coupling nucleotide hydrolysis to the binding of DNA.en-USJournal Article2019-10-0510.1074/jbc.M111.218651