pfam18698: HisK_sensor (This model is not part of the current CDD release)
Histidine kinase sensor domain
The Bacillus subtilis ResD-ResE two-component (TC) regulatory system activates genes involved in nitrate respiration in response to oxygen limitation or nitric oxide (NO). The sensor kinase ResE activates the response regulator ResD through phosphorylation, which then binds to the regulatory region of genes involved in anaerobiosis to activate their transcription. In other words, ResE is involved in sensing signals related to the redox state of the cells. ResE is composed of an N-terminal signal input domain and a C-terminal catalytic domain. The N-terminal domain contains two transmembrane subdomains and a large extra-cytoplasmic loop. Mutational analysis indicate that cytoplasmic ResE lacking the transmembrane segments and the extra-cytoplasmic loop retains the ability to sense oxygen limitation and NO, which leads to transcriptional activation of ResDE-dependent genes. Having said that, it is also proposed that the extra-cytoplasmic region may serve as a second signal-sensing subdomain. This suggests that the extracytoplasmic region could contribute to amplification of ResE activity leading to the robust activation of genes required for anaerobic metabolism in B. subtilis. This entry represents the extracytoplasmic subdomain. Family members also include SrrB found in S. aureus that is similar to ResE of B. subtilis.
Jiyao W et al.(2023). "The conserved domain database in 2023.",