Dimerization region of soluble guanylate cyclase characterized by bimolecular fluorescence complementation in vivo

The ubiquitously expressed nitric oxide (NO) receptor soluble guanylate cyclase (sGC) plays a key role in signal transduction. Binding of NO to the N-terminal prosthetic heme moiety of sGC results in ∼200-fold activation of the enzyme and an increased conversion of GTP into the second messenger cGMP. sGC exists as a heterodimer the dimerization of which is mediated mainly by the central region of the enzyme. In the present work, we constructed deletion mutants within the predicted dimerization region of the sGC α₁- and β₁-subunit to precisely map the sequence segments crucial for subunit dimerization. To track mutation-induced alterations of sGC dimerization, we used a bimolecular fluorescence complementation approach that allows visualizing sGC heterodimerization in a noninvasive manner in living cells. Our study suggests that segments spanning amino acids α₁363-372, α₁403-422, α₁440- 459, β₁212-222, β₁304-333, β ₁344-363, and β₁381-400 within the predicted dimerization region are involved in the process of heterodimerization and therefore in the expression of functional sGC.