Adenylyl cyclase Rv1625c of Mycobacterium tuberculosis: a progenitor of mammalian adenylyl cyclases

The gene Rv1625c from Mycobacterium tuberculosis encodes a membrane-anchore d adenylyl cyclase corresponding to exactly one-half of a mammalian adenyly l cyclase. An engineered, soluble form of Rv1625c was expressed in Escheric hia coli. It formed a homodimeric cyclase with two catalytic centers. Amino acid mutations predicted to affect catalysis resulted in inactive monomers . A single catalytic center with wild-type activity could be reconstituted from mutated monomers in stringent analogy to the mammalian heterodimeric c yclase structure. The proposed existence of supramolecular adenylyl cyclase complexes was established by reconstitution from peptide-linked, mutation- inactivated homodimers resulting in pseudo-trimeric and -tetrameric complex es. The mycobacterial holoenzyme was expressed successfully in E.coli and m ammalian HEK293 cells, i.e. its membrane targeting sequence was compatible with the bacterial and eukaryotic machinery for processing and membrane ins ertion. The membrane-anchored mycobacterial cyclase expressed in E.coli was purified to homogeneity as a first step toward the complete structural elu cidation of this important protein. As the closest progenitor of the mammal ian adenylyl cyclase family to date, the mycobacterial cyclase probably was spread by horizontal gene transfer.