[Structural-functional organization of the adenylyl cyclases in unicellular eukaryotes and molecular mechanisms of its regulation].

At the present time, adenylyl cyclases (ACs)--the enzymes, catalyzing the formation of second messenger cAMP, were found in yeasts and related fungi, amoeba Dictyostelium discoideum, flagellates, malaria plasmodium, ciliates. However, structural-functional organization of the ACs and molecular mechanisms of its regulation are different to great extent. The scores of structurally related ACs, one time penetrating the membrane and possessing the receptor function, were identified in flagellates. Three types of ACs, strongly differed in the topology, the domain organization and the sensitivity to regulatory molecules and physical factors, were found in amoeba D. discoideum. One of them (AC-A) is close to membrane-bound ACs of the mammals and can be regulated by extracellular cAMP. It was shown that the enzymes of the yeasts, lacking the transmembrane domains, formed the intermolecular complexes, which were stabilized by the interactions between leucine-rich repeat regions. The data presented in the review give evidence that the main molecular mechanisms of the functioning of vertebrate ACs were formed in unicellular organisms and fungi. At the same time the structure and functions of the ACs of the lower eukaryotes are strongly varied. It can be connected with the special features of life cycle of the lower eukaryotes and with the realization of different models of functioning and regulation of cAMP-dependent cascades at the earlier steps of evolution.