Ruthenburg, Alexander J.Graybosch, Daina M.Huetsch, John C.Verdine, Gregory L.2019-10-092005Ruthenburg, Alexander J., Daina M. Graybosch, John C. Huetsch, and Gregory L. Verdine. 2005. “A Superhelical Spiral in the Escherichia ColiDNA Gyrase A C-Terminal Domain Imparts Unidirectional Supercoiling Bias.” Journal of Biological Chemistry280 (28): 26177–84. https://doi.org/10.1074/jbc.M502838200.0021-92581083-351Xhttp://nrs.harvard.edu/urn-3:HUL.InstRepos:41511290DNA gyrase is unique among type II topoisomerases in that its DNA supercoiling activity is unidirectional. The C-terminal domain of the gyrase A subunit (GyrA-CTD) is required for this supercoiling bias. We report here the x-ray structure of the Escherichia coli GyrA-CTD ( Protein Data Bank code 1ZI0). The E. coli GyrA-CTD adopts a circular-shaped beta-pinwheel fold first seen in the Borrelia burgdorferi GyrA-CTD. However, whereas the B. burgdorferi GyrA-CTD is flat, the E. coli GyrA-CTD is spiral. DNA relaxation assays reveal that the E. coli GyrA-CTD wraps DNA inducing substantial (+) super-helicity, while the B. burgdorferi GyrA-CTD introduces a more modest (+) superhelicity. The observation of a superhelical spiral in the present structure and that of the Bacillus stearothermophilus ParC-CTD structure suggests unexpected similarities in substrate selectivity between gyrase and Topo IV enzymes. We propose a model wherein the right-handed ((+) solenoidal) wrapping of DNA around the E. coli GyrA-CTD enforces unidirectional (+) DNA supercoiling.en-USJournal Article2019-10-0910.1074/jbc.M502838200