A variant of the alpha 2 subunit of soluble guanylyl cyclase contains an insert homologous to a region within adenylyl cyclases and functions as a dominant negative protein.

A variant of the alpha 2 subunit of soluble guanylyl cyclase (alpha 2i) containing 31 additional amino acids was identified in a number of cell lines and tissues. The in-frame sequence of the insert was within the proposed catalytic domain of guanylyl cyclases and was homologous to a region within the putative catalytic domain of adenylyl cyclases. Messenger RNA for the new variant was detected in some but not all cell lines and tissues expressing the alpha 2 subunit. The novel form, as well as the alpha 2 subunit lacking the insert, were coexpressed with the beta 1 subunit in Sf9 and COS-7 cells; alpha 2/beta 1 coexpression yielded a NO-sensitive recombinant protein, whereas the coexpressed alpha 2i/beta 1 subunits exhibited no guanylyl or adenylyl cyclase activities. Because both subunits (alpha 2i/beta 1) copurified, the novel variant retains its ability to heterodimerize. In coexpression experiments, the alpha 2i subunit competed with the alpha 2 subunit for dimerization with the beta 1 subunit, thereby reducing alpha 2/beta 1-catalyzed guanylyl cyclase activity. These data show that the novel variant functions as a dominant negative protein and that post-transcriptional mRNA processing represents a potential mechanism for regulation of NO-sensitive guanylyl cyclase activity.