Globin-coupled sensor proteins are a family of multidomain proteins which link sensory input to a diverse array of downstream effectors. The extremophile Thermus aquaticus encodes a GCS protein (TaqGCS) with putative diguanylate cyclase activity, which has not been isolated or characterized to date. AfGcHk was also purified to compare the mechanism of signal transduction between GCS proteins. Discovering unique proteins across the GCS family can further elucidate their role in sensory perception and signal transduction.