Solution structure of the homodimeric core domain of Escherichia coli histidine kinase EnvZ

Escherichia coli osmosensor EnvZ is a protein histidine kinase that plays a central role in osmoregulation, a cellular adaptation process involving th e His-Asp phosphorelay signal transduction system. Dimerization of the tran smembrane protein is essential for its autophosphorylation and phosphorelay signal transduction functions. Here we present the NMR-derived structure o f the homodimeric core domain (residues 223-289) of EnvZ that includes His 243, the site of autophosphorylation and phosphate transfer reactions. The structure comprises a four-helix bundle formed by two identical helix-turn- helix subunits, revealing the molecular assembly of two active sites within the dimeric kinase.