Ciliate pheromone structures and activity: a review

As in animals and other multicellular organisms, protozoan ciliates communicate via diffusible signalling pheromones. These pheromones have been identified in the culture supernatant of various species. However, their isolation and definitive structural characterization have been achieved only in species of Blepharisma and Euplotes. With the exception of the two B. japonicum pheromones represented by a tryptophan-related molecule and a glycoprotein, all the other pheromones isolated from Euplotes species are proteins that vary in extension between 38 and 109 amino acids. They form species-specific families of structurally homologous members, in full accord with their multi-allelic determination at an apparently single genetic locus. The determination of the Nuclear Magnetic Resonance (NMR) solution structures of E. raikovi and E. nobilii pheromones has provided direct evidence that, although structurally unique, Euplotes pheromones adopt a common, speciesspecific three-helix folding. This close structural homology among members of the same family well accounts for the pheromone capacity to compete with one another in cell receptor binding reactions and elicit context-dependent, autocrine (growth-promoting) or paracrine (mating-inducing) cell responses.