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Crystal Structures of Escherichia coli Topoisomerase IV ParE Subunit (24 and 43 Kilodaltons): a Single Residue Dictates Differences in Novobiocin Potency against Topoisomerase IV and DNA Gyrase. Steven Bellon, 2004.Topoisomerase IV and DNA gyrase are related bacterial type II topoisomerases that utilize the free energy from ATP hydrolysis to catalyze topological changes in the bacterial genome . The essential function of DNA gyrase is the introduction of negative DNA supercoils into the genome, whereas the essential function of topoisomerase IV is to decatenate daughter chromosomes following replication . Here, we report the crystal structures of a 43-kDa N-terminal fragment of Escherichia coli topoisomerase IV ParE subunit complexed with adenylyl-imidodiphosphate at 2.0-Å resolution and a 24-kDa N-terminal fragment of the ParE subunit complexed with novobiocin at 2.1-Å resolution . The solved ParE structures are strikingly similar to the known gyrase B (GyrB) subunit structures . We also identified single-position equivalent amino acid residues in ParE (M74) and in GyrB (I78) that, when exchanged, increased the potency of novobiocin against topoisomerase IV by nearly 20-fold (to 12 nM) . The corresponding exchange in gyrase (I78 M) yielded a 20-fold decrease in the potency of novobiocin (to 1.0 µM) . These data offer an explanation for the observation that novobiocin is significantly less potent against topoisomerase IV than against DNA gyrase . Additionally, the enzyme kinetic parameters were affected . In gyrase, the ATP Km increased  5-fold and the Vmax decreased
30% . In contrast, the topoisomerase IV ATP Km decreased by a factor of 6, and the Vmax increased
2-fold from the wild-type values . These data demonstrate that the ParE M74 and GyrB I78 side chains impart opposite effects on the enzyme's substrate affinity and catalytic efficiency .
Conserved Amplification of Chemotactic Responses through Chemoreceptor Interactions. Allison C. Lamanna, 2002.Many bacteria concentrate their chemoreceptors at the cell poles . Chemoreceptor location is important in Escherichia coli, since chemosensory responses are sensitive to receptor proximity . It is not known, however, whether chemotaxis in other bacteria is similarly regulated . To investigate the importance of receptor-receptor interactions in other bacterial species, we synthesized saccharide-bearing multivalent ligands that are designed to cluster relevant chemoreceptors . As has been shown with E . coli, we demonstrate that the behaviors of Bacillus subtilis, Spirochaete aurantia, and Vibrio furnissii are sensitive to the valence of the chemoattractant . Moreover, in B . subtilis, chemotactic responses to serine were increased by pretreatment with saccharide-bearing multivalent ligands . This result indicates that, as in E . coli, signaling information is transferred among chemoreceptors in B . subtilis . These results suggest that interreceptor communication may be a general mechanism for modulating chemotactic responses in bacteria .
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