Lipid regulation of adenylyl cyclase Rv1625c from Mycobacterium tuberculosis by its membrane-domain receptor

The regulation of mammalian adenylyl cyclases by G-protein-coupled receptors and the Gsα subunit of trimeric G-proteins has been extensively studied, whereas little is known about the regulation of their closely related bacterial cyclases. Here, we focused on the regulation of the adenylyl cyclase Rv1625c from Mycobacterium tuberculosis H37Rv. Rv1625c is a progenitor of mammalian congeners. Exclusively C₁₈-mono-unsaturated fatty acids, such as the cis- and trans-isoforms of oleic and vaccenic acids, inhibited the Rv1625c holoenzyme with IC₅₀ concentrations around 10 μm. The saturated C₁₈ fatty acid stearic acid was inactive. A soluble Rv1625c construct, which lacked the membrane domain, was not affected by the mono-unsaturated C₁₈ fatty acids, i.e., the inhibition required the presence of the membrane domain, indicating a receptor-ligand interaction. Surprisingly, fatty acid inhibition of Rv1625c was strictly dependent on magnesium ions (Mg²⁺) as a divalent cation for the substrate adenosine triphosphate (ATP). Although manganese ion (Mn²⁺)-ATP as a substrate greatly increased enzyme activity, Mn²⁺ appeared to block intramolecular signal transduction from the membranous receptor domain to the catalytic effector domain. In summary, the results bolster the proposal that adenylyl cyclase regulation by fatty acids is an evolutionarily conserved signaling mode present in bacteria as well as in mammals.