Localized perturbations in cheY structure monitored by NMR identify a chea binding interface

Phosphotransfer between the autophosphorylating histidine kinase CheA and the response regulator CheY represents a crucial step in the bacterial chemotaxis signal transduction pathway. The ¹⁵N-¹H correlation spectrum of CheY complexed with an amino-terminal fragment of CheA exhibits specific localized differences in chemical shifts when compared to the spectrum of uncomplexed CheY. When mapped onto the three-dimensional structure of CheY, these changes define a region distinct from the active site. A single amino-acid substitution within this binding region on CheY, alanine to valine at position 103, significantly decreases the affinity of CheY for CheA. The binding face described by these changes partially overlaps a flagellar switch binding surface previously defined by mutagenesis.