Characterization of a New Class of Receptors: Identifying ligands for the membrane receptors of the class IIIa human adenylate cyclases.

• Applicant: Professor Dr. Joachim E. Schultz
• Subject Area: Pharmacology ; Pharmacy
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 456822801

The membrane anchors of the nine adenylate cyclases in mammals possess a total of 12 alpha-helical transmembrane spans (2 x 6TM). These membrane anchors are evolutionarily conserved for more than half a billion years. Since 1989 discussions took place speculating about a physiological function of the membrane anchors beyond membrane anchoring. For three decades this laboratory has carried out studies in order to assign a physiological role to the membrane anchors, We used the quorum-sensing receptors from Vibrio harveyi and Legionella pneumophila. These receptors are hexahelical in the monomeric proteins which dimerize, i.e. they are almost isosteric to the membrane anchors of the mammalian adenylate cyclases. In addition, lipophilic ligands are known for these quorum-sensing receptors. In chimeras comprising various class III adenylate cyclases and quorum.sensing receptors we demonstrated in 2020 beyond a reasonable doubt that the membrane anchor of mammalian adenylate cyclases can operate as ligand receptors which attenuate the Gsalpha activation of mammalian adenylate cyclases. Currently, the chemical identity of the ligands is unknown. We identified biochemically "ligandactivity" in serum from fish, chicken, cow, and humans, among others. Enrichment of ligands by various purification methods identified acidic lipohilic compounds as ligands. A first lipidomic analysis yielded data which are hints to identify the chemical nature of the ligands in the foreseeable future. This is the first aim of the proposal. Then we wish to characterize biochemically and pharmacologically ligand-receptor interactions for all nine human adenylate cyclase isoforms. We will attempt to identify potential agonists and antagonist based on our knowledge of the chemical identity of peculiar ligands. Adenylatcyclases are known to be regulated by several cytosolic secondary modifications. We will investigate how ligand-receptor controlled regulation and regulation by secondary modifications are interacting. Finally, we will examine the regulation of intracellular cAMP levels in HEK293 cells in order to gain initial indications for physiological actions of adenylate cyclase receptor ligands.

• DFG Programme: Research Grants