Identification of a nonmammalian g(olf) subtype: Functional role in olfactory signaling of airborne odorants in Xenopus laevis

Attempts to identify the G alpha subtypes in the two compartments of the ol factory system from Xenopus, which are supposed to be specialized for detec ting aquatic and volatile odorous compounds, revealed that a G alpha (ol) s ubtype is characteristic for the "water nose," the lateral diverticulum, wh ereas a novel G alpha (s) subtype predominates in the "air nose," the media l diverticulum. The newly identified G alpha (s)-type is more closely relat ed to G alpha (olf) of rat and human than to the known G alpha (s)-isoform of Xenopus; it is therefore considered the first identified nonmammalian G alpha (olf) subtype. Sequence comparison of G alpha (olf) from amphibia and mammals revealed a particular conservation within the alpha -helical domai ns, which are supposed to control the GDP/GTP-exchange rate. The selective expression of different G alpha subtypes in the two anatomically separated and functionally specialized nasal compartments parallels the expression of distinct classes of olfactory receptors. Moreover, biochemical analysis re vealed that stimulation with appropriate odorous compounds elicits the form ation of inositol trisphosphate in the lateral diverticulum. In contrast, c yclic adenosine monophosphate signals were induced in the medial diverticul um, and this response appears to be mediated by the novel G alpha (olf) sub type. The data indicate that olfactory sensory neurons in each of the nasal cavities are equipped not only with defined sets of receptor types but als o with a distinct molecular machinery for the chemo-electrical transduction process. (C) 2001 Wiley-Liss, Inc.