Molecular regulation mechanisms of receptor guanylyl cyclases

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The second messenger cGMP has a key function e.g. in the cardiovascular system and in vision. In mammals, a soluble and several transmembrane receptor guanylyl cyclases (GCs) are activated by nitric oxide and extracellular ligands, respectively. Mammalian GCs have an N-terminal ligand binding domain, a kinase homology domain (KHD), and a catalytic domain homologous to adenylyl cyclases. The KHD acts as a negative regulator and ATP binding, but not hydrolysis, is required in order to relieve its inhibitory effect on catalysis. Another mechanism of regulation of GC is an ATP- and GTP-dependent process proceeding via the small GTPase Rac1, which activates the kinase PAK whose catalytic domain then binds directly to the GC catalytic domain and increases its activity. We propose to study the molecular mechanisms of regulation of GC catalytic domains by small molecules, PAK, and the internal regulator KHD, and how to exploit these mechanisms with artificial modulators. Crystal structures of catalytic domains will be solved in complex with ligands in order to identify differences to ACs and between GC isoforms. We further aim to solve structures of complexes between catalytic domains and PAK and KHD in presence and absence of ATP analogs in order to reveal how PAK activation and ATP binding to the KHD lead to activation of the catalytic domain. We will attempt to exploit our findings for the structure-based design of novel regulator compounds for in vivo studies and drug development.