Two-component systems, consisting of a histidine kinase and a cognate response regulator protein, represent the best-known apparatus for transducing external cues into a physiological response in bacteria. The HWE domain is found in a subset of two-component system kinases, belonging to the same superfamily as Pfam:PF00512 [1] and Pfam:PF07568 [2]. The family was defined by [1] the presence of a highly conserved H residue in the kinase domain and a WxE motif in a C-terminal ATPase domain that is related to Pfam:PF02518. It has been demonstrated to show structural and functional correlation with Pfam:PF07568 [2]. These proteins are found in a variety of alpha- and gamma- proteobacteria, with significant enrichment in the rhizobia.

1: The HWE Histidine Kinases, a New Family of Bacterial Two-Component Sensor Kinases with Potentially Diverse Roles in Environmental Signaling. Karniol B, Vierstra RD; J Bacteriol 2004;186:445-453. PMID:14702314

2: Structure and function of HWE/HisKA2-family sensor histidine kinases. Herrou J, Crosson S, Fiebig A; Curr Opin Microbiol. 2017;36:47-54. PMID:28193573