Energy Coupling in Escherichia coli DNA Gyrase: the Relationship between Nucleotide Binding, Strand Passage, and DNA Supercoiling

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Abstract
Binding of the nonhydrolyzable ATP analogue 5'-adenylyl-beta, gamma-imidodiphosphate (ADPNP) to Escherichia coli DNA gyrase can lead to a limited noncatalytic supercoiling of DNA. Here we examine the efficiency of coupling between ADPNP binding and the change in linking number either of positively or negatively supercoiled plasmid DNA or of small DNA circles. The coupling efficiency varies from 100% (delta Lk = -2 per gyrase tetramer, a stoichiometry of 1) with positively supercoiled substrates under certain reaction conditions to an undetectably low value with moderately negatively supercoiled substrates (sigma = -0.046) or small circular substrates. Furthermore, the rate of ADPNP binding to the gyrase-DNA complex is also dependent on the topological state of the DNA; the previously observed slow binding of ADPNP to the complex of gyrase with linear DNA is accelerated 16-fold when the substrate DNA is negatively supercoiled, suggesting a functional interaction between the nucleotide-binding and DNA-binding domains which is independent of the strand-passage process. The implications for the normal ATP-dependent supercoiling reaction of the enzyme are considered and the results discussed in terms of current mechanistic models for DNA gyrase action and the possible in vivo roles of the enzyme.

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