Guanylyl cyclase-D in the olfactory CO2 neurons is activated by bicarbonate

Atmospheric CO2 is an important environmental cue that regulates several types of animal behavior. In mice, CO2 responses of the olfactory sensory neurons (OSNs) require the activity of carbonic anhydrase to catalyze the conversion of CO2 to bicarbonate and the opening of cGMP-sensitive ion channels. However, it remains unknown how the enhancement of bicarbonate levels results in cGMP production. Here, we show that bicarbonate activates cGMP-producing ability of guanylyl cyclase-D (GC-D), a membrane GC exclusively expressed in the CO2-responsive OSNs, by directly acting on the intracellular cyclase domain of GC-D. Also, the molecular mechanism for GC-D activation is distinct from the commonly believed model of release from repression'' for other membrane GCs. Our results contribute to our understanding of the molecular mechanisms of CO2 sensing and suggest diverse mechanisms of molecular activation among membrane GCs.