FIGURE 1.

Alignment of heme-bound oxygen-sensing and functional domains of the heme-based oxygen sensors. Left, the C-terminal HK domain in the two-component system containing N-terminal heme-bound globin, PAS, or GAF domains. Right, the C-terminal functional domains associated with MCP, c-diGMP homeostasis (DGC, synthesis; and PDE, degradation), and unknown functions (transmembrane (TM)) containing the N-terminal heme-bound globin or PAS domain. GCSs are defined as chimeric proteins composed of heme-bound globin and functional domains (14–18). Note that EcDOS and FixL have two tandem PAS domains; the heme iron complex is bound to the first PAS domain in EcDOS and to the second PAS domain in FixL. Similarly, DevS and DosT have two tandem GAF domains; in both cases, the heme iron complex is bound to the first GAF domain. Note that globin folds are not always localized at the N terminus but are inserted into diverse regions, as predicted from the amino acid sequences of sensor globins that are yet to be characterized (14–18). AxPDEA1, A. xylinum PDEA1.