Research ArticleStructural Biology

Architecture of the complete oxygen-sensing FixL-FixJ two-component signal transduction system

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Sci. Signal.  10 Apr 2018:
Vol. 11, Issue 525, eaaq0825
DOI: 10.1126/scisignal.aaq0825

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Signal relay through a two-component system

In two-component systems, a sensor histidine kinase undergoes autophosphorylation and transfers a phosphate group to its cognate response regulator, which then mediates cellular responses by binding to DNA, performing enzymatic reactions, or interacting with other proteins. In the FixL-FixJ two-component system of the plant root nodule symbiont Bradyrhizobium japonicum, the histidine kinase FixL undergoes autophosphorylation only when it is not bound to oxygen. This ensures that its cognate response regulator FixJ stimulates the expression of genes required for nitrogen fixation only under low-oxygen conditions. Wright et al. combined high- and low-resolution structural analyses with modeling techniques and functional analysis to generate a model of signal relay through the FixL-FixJ two-component system. The model shows how the dissociation of oxygen from FixL stimulates FixL autophosphorylation and phosphotransfer from FixL to FixJ.