Nuclear Magnetic Resonance Assignments and Global Fold of a CheY-Binding Domain in CheA, the Chemotaxis-Specific Kinase of Escherichia coli

CheA is the histidine autokinase in the Escherichia coli chemotaxis signal transduction pathway responsible for coupling of signals received by transmembrane receptors to the response regulators CheY and CheB. Here NMR spectroscopy is used to study a 14 kDa fragment of CheA, residues 124-257, that binds the response regulator CheY. Backbone atom resonance assignments were obtained by analysis of 3D HNCACB, 3D CBCA(CO)NH, and HNCO spectra, whereas side-chain assignments were obtained primarily by analysis of 3D H(CCO)NH, 3D C(CO)NH, 3D HCCH-TOCSY, and 3D ¹H,¹⁵N TOCSYHSMQC spectra. NOE cross peak patterns and intensities as well as torsion angle restraints were used to determine the secondary structure, and a low-resolution structure was calculated by hybrid distancegeometry simulated annealing methods. The CheA124-257 fragment consists of four antiparallel β strands and two helices, arranged in an “open-faced β-sandwich” motif, as well as two unstructured ends that correspond to domain linkers in the full-length protein. The ¹⁵N-¹H correlation spectrum of ¹⁵N-labeled CheA124-257 bound to unlabeled CheY shows specific localized changes that may correspond to a CheY-binding face on CheA.