Identification of a nonmammalian Golf subtype: functional role in olfactory signaling of airborne odorants in Xenopus laevis.

Attempts to identify the Galpha subtypes in the two compartments of the olfactory system from Xenopus, which are supposed to be specialized for detecting aquatic and volatile odorous compounds, revealed that a Galpha(o1) subtype is characteristic for the "water nose," the lateral diverticulum, whereas a novel Galpha(s) subtype predominates in the "air nose," the medial diverticulum. The newly identified Galpha(s)-type is more closely related to Galpha(olf) of rat and human than to the known Galpha(s)-isoform of Xenopus; it is therefore considered the first identified nonmammalian Galpha(olf) subtype. Sequence comparison of Galpha(olf) from amphibia and mammals revealed a particular conservation within the alpha-helical domains, which are supposed to control the GDP/GTP-exchange rate. The selective expression of different Galpha subtypes in the two anatomically separated and functionally specialized nasal compartments parallels the expression of distinct classes of olfactory receptors. Moreover, biochemical analysis revealed that stimulation with appropriate odorous compounds elicits the formation of inositol trisphosphate in the lateral diverticulum. In contrast, cyclic adenosine monophosphate signals were induced in the medial diverticulum, and this response appears to be mediated by the novel Galpha(olf) subtype. The data indicate that olfactory sensory neurons in each of the nasal cavities are equipped not only with defined sets of receptor types but also with a distinct molecular machinery for the chemo-electrical transduction process.