Guanylyl cyclase/PSD-95 interaction: targeting of the nitric oxide-sensitive alpha2beta1 guanylyl cyclase to synaptic membranes.

The signaling molecule nitric oxide (NO) exerts most of its effects by the stimulation of the NO-sensitive guanylyl cyclase. Two isoforms of the NO receptor molecule exist: the ubiquitously occurring alpha(1)beta(1) and the alpha(2)beta(1) with a more limited distribution. As the isoforms are functionally indistinguishable, the physiological relevance of these isoforms remained unclear. The neuronal NO synthase has been reported to be associated with PSD-95. Here, we demonstrate the interaction of the so far unnoticed alpha(2)beta(1) isoform with PSD-95 in rat brain as shown by coprecipitation. The interaction is mediated by the alpha(2) C-terminal peptide and the third PDZ domain of PSD-95. As a consequence of the PSD-95 interaction, the so far considered "soluble" alpha(2)beta(1) isoform is recruited to the membrane fraction of synaptosomes, whereas the alpha(1)beta(1) isoform is found in the cytosol. Our results establish the alpha(1)beta(1) as the cytosolic and the alpha(2)beta(1) as the membrane-associated NO-sensitive guanylyl cyclase and suggest the alpha(2)beta(1) isoform as the sensor for the NO formed by the PSD-95-associated neuronal NO synthase.